Steam requires to provide finished product and support. Apart from the libre games, there's a bunch of Linux ports that will never get into Steam because devs can't/don't want to support Linux beyond porting their game.
Humble Bundle is not an indicator. It's great that Linux users spend more, but if you'll take Windows or console game market in account, $2 per game spent by Linux users is nothing. All these games on Steam together worth around $60.
KDE4 runs just fine with 512MB RAM and modern Android devices have even more. If you'll read the thread you've linked, you'll see that it's an openSuSE issue which has a lot of pre-enabled KDE components that are not needed on a tabled (like semantic desktop).
I've been using GTalk for years but it kind of sucks when you're using it with 3rd-party client. Most of it's features and XEPs are GTalk-exclusive and at the same time it doesn't support popular modern XEPs like "publish tune".