Cost alone? Nah, surely not. Not that SQL Server is cheap any more, it isn't, but DB2 is hardly the low cost alternative. It's either politics, or some other piece of functionality. Cost doesn't make sense.
"The credit belongs to the man who is actually in the arena, whose face is marred by dust and sweat and blood"
- Theodore Roosevelt
Author of:
SQL Server Execution Plans
SQL Server Query Performance Tuning