Well, if someone wants to play XNA is clear that he must have installed it :)
little by little it will be installed on all systems of interest I would guess
why would a gamer care if a game is made with XNA, Blitzmax, or just C++? They want to just play. I'm referring to PC games of course (360 is a different matter). Just from personal experience the few little demos and small games I made with XNA I've received e-mails regarding how to get the game up and running beecause it didn't 'just run'
.NET shouldn't be a problem, should be installed on anything that supports XNA unless its a cool morron with disabled autoupdate. Many games today use it for different aspects like the game starters etc. So little of a problem as well
true .NET is a little more wide-spread but I hate to release something knowing someone might run into the issue and then having to provide them with a 22MB dl for a 5-10MB game (not to mention the install time).
DX updates are standard due to the bimonthly DX update periodicity. This is needed for pure DX9 games as well.
I figured this was the case also. But surprisingly, even I had problems getting XNA running on some of my gaming rigs (which played games such as bf2142 and HL2). Despite having an 'updated' DX i still had to run the web installer to get a minor update to DX. Again, another loop to jump through (as far as I know, DX doesn't auto-update). This particular issue however, could have changed since the release of XNA 2.0
-> either offer the links or if you distribute through disk, put it on it as auto installers.
last I checked you weren't technically 'allowed' to include the DX installer (and maybe possibly the .NET installer as well, not too sure though) into your own installers and the best you could do was provide a DL link. And also if you do put the installers there, it just bloats your installer (22 for .net, and however big the DX update would be). As opposed to just being able to simply zip up a blitzmax game and have good confidence that it'll run on most PC's.
I probably come off as hating XNA, but that's certainly not the case. I really enjoy using it, and I'm still developing with it. But in the current scheme of things, XNA seems more targetted at 360 rather than PC distribution, whereas blitzmax is setup for easy PC distribution.