It's not really B&D: when you recieve a request, you have to keep in mind what verb was used because each verb guarantees different kinds of behaviour. For instance, it's one thing to treat GET and POST requests identically if what you're doing to process the request fits the kind of behaviour that's acceptable in response to such a request, such as, say, displaying a page, but quite another thing if they don't, such as Anders' example of an application allowing items to be deleted with GET requests.
However, as Ian outlined, such matters are a matter for a higher-level framework than WSGI and deciding them at WSGI's level would complicate the interface between it and the application or framework sitting on top of it.
It is something that matters quite a bit, but because of HTTP itself and not some misplaced desire for B&D. It's something which ought to be in the minds of any application developer because part of developing a good application is using the underlying protocol correctly. It's nothing to do with forcing a programming model and everything to do with passing the request onto another lump of code smart enough to really know what to do with it.