I guess Azure may be an option I have never done testing to see how responsive their database in the cloud can be to very high loads.
Oh yeah, I should point out that I haven't checked out Azure personally, but I consider all cloud providers incompatible with Bitcoin security requirements (which is unfortunate because my Linode VPS is great.)
I agree there is value in open platforms and SQL Server is one of Microsofts most expensive and most restricted products. I think this got somewhat sidetracked (partially my fault). The original claim (not by you) was that asp.net doesn't scale and is expensive. asp.net can use any RDBMS as a backend and is highly scalable. For a new startup SQL Server is likely the easiest route as there is going to be some skills overlap but beyond 64GB or 16 cores I agree there is significant cost. It is something a startup would need to consider.
As a personal note:
To avoid vendor lock in whenever possible I try to keep the database code as ANSI SQL compliant as possible to allow a "backdoor" by keeping the migration costs & complexity to a minimum.
Nah we should blame gweedo instead.

I wasn't clear enough in my original post since I do think that ASP.NET is OK for scaling technically, but I just wanted to point out some gotchas and hidden costs on the business side. Granted those are probably a bit out of the range of a Bitcoin business for a while, but I can always hope for crazy volume...
Also,
RAM is incredibly cheap now! I'm sure MS will change their licensing tune if they can foresee a hit to the Server and Tools business.