Logging in with a non-gmail account I got here an ePad running Android 2.3 and I want to set up Market on it for its owner. He doesn't have a Gmail account, neither he wants one. I have just made a Google account that is associated with an existing ISP email address.

I can successfully login with my personal email address (someone at mydomain.org) from my Iconia tablet, but this doesn't seem to be the case of older Android versions. I made the Google account from the plain old ISP address because I thought it would have worked like my case!

Am I missing something about logging in to Market with a non-gmail account? Googling around I found that somebody fixed by joining Google+, so I did with the tablet's owner, but the tablet still requires me to open a new account with a gmail email.

Thank you
You can only log in to the market with either your gmail account, or an account hosted with Google Apps for your domain. 

This is not just to authenticate you, information is synced between your device and google servers. If you don't have an account with them, they don't know who you are. You said that you can login with your personal email address (someone at mydomain.org). I am going to guess that mydomain.org is hosting the email on google apps for your domain.