ASP.NET Custom Errors and Status Codes
Chris Love has a good post about error handling in ASP.NET. There's a lot of debate (and perhaps confusion) about properly implementing error handling and URL rewriting (see this post) but Chris has some good insight on this.
The bottom line, in my opinion, is that the behavior is an architectural decision. The status code and page returned may be variable based on the circumstance -- was there truly an unhandled exception? What about when a product ID no longer exists? Should we redirect to closely matching products, assuming we retain information on what the old product was?