When you're pushing triple digits of open tabs, it can definitely become an issue. Plus the web interface runs on flash and support isn't great for Linux, even chrome's Pepper version has a ton of issues.
edit: Point being that playing an mp3 should never freeze any system built in this millennium, and yet it does. So this is a bit of a workaround to avoid that. Plus with this setup you can enable global media keys/hotkeys and get a lot more control over playing your music.
I'm certainly not saying what they have is ideal, so don't take offense on that note. I welcome a native-ish client ala Spotify since I foolishly subscribe to both.
But as someone who keeps their open tabs in the double digits (although pushing it sometimes), I've not encountered much playback issue.
I haven't run into any issues on my i5 machine, but on a core2duo machine it was many many times a day I had to kill firefox/plugin-container just in time or I'd have to reboot.
Heh, I actually don't have any icons at all, I just like having everything I need out in front of me so I use awesome window manager and open a bunch of windows with tons of tabs, multitasking at its finest.
