idolw - 9:51 am on Feb 11, 2010 (gmt 0)
All of us look at this from webmaster/business point of view.
There are many people who use internet only for fun and they'll be happy to have fun features in their gmail. Instead of logging to facebook, twitter, hi5, etc. they'll just log into gmail and see both: emails from their friends and what friends are up to right now.
Google must have been asking twitter to put adsense on all tweets but twitter was "looking for a business model". Now they built better twitter alone and will not need to share the revenue.