Consumers who use the Chrome browser on their iPhone aren’t really using Google Inc.’s Chrome: They are using Safari with a Chrome skin around it.

Retailers looking to give shoppers a feature-rich, robust and fast mobile shopping experience should take note because that means that some features developers code for a mobile site may not work for iPhone shoppers.

Among Apple Inc.’s long list of app store review guide lines for developers is the statement, “Apps that browse the web must use the iOS WebKit framework and WebKit Javascript.” Therefore, any app for iPhone that functions as a browser is really using Safari (Apple’s browser) web browsing technology.

This “closed ecosystem” is nothing new for Apple, but Safari’s browsing technology lags its browser competitors, including Chrome. For example, mobile sites developed with HTML5 running on a mobile Chrome browser can access a consumer’s camera, whereas Safari does not support this function. And so, mobile sites on the Chrome app on an iOS device also do not have this function.

Plus, Apple has the majority of smartphone devices in the U.S., as 44.6% of U.S. smartphone subscribers 13 and older have an iPhone, 28.3% have a Samsung device, 10.0% LG, 4.3% Motorola and 2.2% HTC, according to analytics firm comScore Inc. as of February 2017. That means that almost half of smartphone users don’t have the the most up-to-date browsing technology.

“Apple should be leading the charge on mobile browsers, not playing a follower role,” says Ted Schadler, a Forrester Research Inc. vice president and principal analyst. “Apple’s customers need all browsers to work brilliantly on iPhones and iPads, and today they don’t.”

While a mobile web camera function may not seem like a big deal, iPhone-using consumers can’t fully experience the next wave mobile web development—Progressive Web Apps. PWAs are a Google mobile web technology that promises to have the look and customer engagement of an app, but in a mobile website.

“Progressive web apps are the future of the web,” says Julie Ask, vice president and principal analyst at Forrester. The quick functioning websites are ideal for the mobile web and a good alternative for an app for lower-frequency shoppers, she says.

For example, progressive web apps allow retailers to send web push notifications, allow shoppers to add an icon for that retailer’s site to their smartphone home screen without having to download the app, and PWAs are typically much faster than traditionally mobile websites. Except none of these capabilities are available on Safari, which means not on iPhones.

Although few retailers have adopted progressive web app mobile technology, a few who have used the technology have generated great results. Cosmetics retailer Lancôme, a brand of L’Oréal Paris, for example, updated its mobile site to use progressive web app technology, which helped boost its mobile sales 16% year over year, says Malik Abu-Ghazaleh, vice president, digital marketing and e-commerce. Peer-to-peer marketplace 5miles, which also updated its mobile site to a progressive web app, found that shoppers spend 20% more time on the PWA mobile site than they did on the previous mobile site, and on average are looking at seven products per visit, compared with viewing five products per web visit previously,  says Lucas Lu, CEO and founder of 5miles.

To dig into the nitty gritty:  Progressive Web Apps can quickly load on the mobile web for several reasons, including its “service worker” technology, which Safari does not currently support. Service workers fetch content in the background on a separate computer processing unit (CPU) than the CPU running the website and completing the tasks the consumer is requesting. Each smartphone has between two, three or four CPUs, says Peter McLachlan, chief product officer at mobile commerce vendor Mobify.

Experts say Apple lags in browser technology because of its lucrative app business. Forrester Research estimates that of the billions in revenue that Apple makes each quarter in the “services” line item, much of that is from apps and content consumed in apps, and little to no revenue comes from websites. “There’s a clear financial incentive for Apple to improve apps but little financial incentive to improve the browser,” the research firm writes in its recent white paper, “A Billion Mobile Site Spark No Joy.”

“In our interviews with major brands, tech vendors, and some brilliant web developers, it’s become clear to us that Apple’s slow adoption of mobile web technology is holding us all back,” Forrester writes.

“The major issue is Apple’s minimal participation in the browser standards process and the slow adoption of important new standards like service workers,” Schadler adds.

Google and Apple did not respond to requests for comment for this article.

Brian Klais, founder and president of Pure Oxygen Labs, a mobile marketing and mobile search engine optimization firm, agrees noting that the technology is a point of contention for Google and Apple.

“Apple wants developers building iOS apps to grow the iOS device halo,” Klais says. “Google views PWAs as keeping the web open for crawling and indexing—core to Google’s business. So, a lot of PWA benefits aren’t available on iOS at this time, such as local device caching, offline viewing, smart banners to install or push notifications.” Like any other website, Google bots can easily crawl the content on progressive web apps, however, it takes more for retailers to code their app to allow Google to crawl it and then index it in search results–work that retailers may not do.

Klais points to Safari’s lack of support for PWA’s as a main reason why he doesn’t anticipate mass adoption of the mobile design method in the next few years.