Why did 37 Signal’s Basecamp price double unannounced?

basecamp37 Signals very quietly doubled their basic entry fee for Basecamp from $24 to a whopping $49/month. There is no explanation offered on the Basecamp or 37 Signals website.

100% is a massive increase, so something is definitely up. Pat Pichette at Mercury Grove offered some theories:

1. They no longer have interest in catering to small businesses. Small businesses are no longer a target.  Their focus is to gain market share in the enterprise market.
2. They are feeling so confident that their software will sell, even with a 100% price increase.
3.Something big is about to happen. An acquisition? 37Signals going public?  

I can’t see the change having anything to do with cost. They can easily scale the number of users without a large increase in cost (unless they are struggling with support issues, and the small accounts are no longer worth the trouble).

Why do you think they doubled the fee?