Because it's a robust and feature rich database/tool-set thats great to develop on and gives me peace of mind. It's been a while since I used MySQL but the database and it's tools left me underwhelmed. I found that I could be more productive with SQL server. I haven't tried Postgres.
I guess I like to think if my databases grow too large for the free version that's a good problem to have. It's not that bad a "time-bomb" to me. Many sites will never need the paid version - especially the ones small enough to be so cost sensitive.
I do backups using a windows scheduled batch file that runs sqlcmd.exe (part of sql express). Slightly hackish but it gets the job done.
Anyway, I hope that articles and interviews like yours do make MS lower the price of SQL standard, but people shouldn't dismiss the MS platform based on cost when in many cases it could be almost free.
I guess I like to think if my databases grow too large for the free version that's a good problem to have. It's not that bad a "time-bomb" to me. Many sites will never need the paid version - especially the ones small enough to be so cost sensitive.