Re: Too much analysis, the main reason is obvious.
I believe it's a bit more complex than that.
1) If you order a home edition as most end-users are likely to do, you're stuck with Windows 8. I just went to Dell's website (US, since that is where I live) and tried a sample order of an Inspiron 15 (just at random, it's a popular laptop). It comes with Windows 8, and there are no options to choose anything else. I'd consider Dell a pretty major vendor.
2) If you buy a machine with Win 8 Pro, you have downgrade rights to Windows 7 Professional or Windows Vista Business (see http://www.microsoft.com/oem/en/licensing/sblicensing/pages/downgrade_rights.aspx). I still doubt the PC vendor will install these for you, but for a business with an IT dept, they're
likely to install their own image anyway.
So, no, most vendors will not ship Windows 7 installed any more, and depending on what you buy, you may or may not have the option to downgrade.