It's not about detecting features. It's about testing: When you're developing a web app, each new browser you choose to support increases your testing time: starting out developing for chrome, adding safari support usually is just a formality. adding firefox support means a couple extra hours of testing, but everything usually works. adding opera support means your tests are going to start failing, and a bunch more work.
I'm picking on websockets because that's what's been annoying me at work lately, but it's just an example. the myspace demo doesn't even use websockets, it's totally irrelevant, but websocket support is a good cursory indication of whether or not it is a modern browser, and therefore how much development time will be added by officially supporting it.
I'm picking on websockets because that's what's been annoying me at work lately, but it's just an example. the myspace demo doesn't even use websockets, it's totally irrelevant, but websocket support is a good cursory indication of whether or not it is a modern browser, and therefore how much development time will be added by officially supporting it.