The media is one aspect of why, but there is another bigger reason why. As of now there is still some compatibility issues with drivers. This will all work its self out with hardware manufactures getting a chance to get their drivers working. Also, many businesses have apps that were created in house or purchased for a very specific purpose. By releasing to businesses it gives the businesses a chance to test out these apps and make any changes to them that they need. Also Microsoft is expecting that many businesses will be installing Vista in isolated computer, not the entire network. If anything goes wrong IT professionals are much more likely to give Microsoft a knowledgeable response rather than a consumer who would just say "it doesn't work".
So pretty much it just deals with bugs and compatibility.
Why the hell would Microsoft release Vista to business first when most respectable IT departments will wait until an OS is proven somewhat stable and reliable before migrating their organizations to it? Most businesses waited a year or so before adopting XP. We just got 2003 server last year. It doesn?t make much sense, unless hard media is not in sufficient production to warrant a standard consumer release. I believe that Microsoft would stand to make much more in sales by releasing to standard consumers first. Oh, and who had the name first: Creative Zen or Microsoft Zune? You would think that they would pick something slightly more unique.