Are you serious? Do you really think that the Windows platform can't scale to handle a few million users and a few million hits/day? Depending on how CPU and database intensive his app is, it's likely that he could scale that far on a single physical server. 8 cores + 8GB of RAM will take you far, even on Microsoft.
Appengine lets someone who'se never heard of load-balancing or database replication do the Royal Wedding website:
If you're telling me you'd be comfortable hosting that on a Windows VM... well, let's just say you wouldn't have enjoyed the day much!
We have no idea what this guy is building, but needing that sort of scalability is not unheard of. I myself have a neat application that could conceivably be mentioned on Oprah, and if it happens I'll be popping champagne corks instead of bloodvessels - I'm on Appengine.