It's an easy feature to implement (Just add an element to <head>: "<meta name="apple-mobile-web-app-capable" content="yes" />"). The downside is that going to

It's an easy feature to implement (Just add an element to <head>: "<meta name="apple-mobile-web-app-capable" content="yes" />"). The downside is that going to other domains/subdomains from a webapp launched that way forces a user into Safari anyways, through a somewhat jarring app-switch-transition. Since Google has an ecosystem of mobile apps they'd like you to switch between they don't want you to feel trapped in just one at a time.