This is a fair question. Please allow me to clarify. While I tend to agree with you about the likelihood of refs accepting supplements, it's misleading to claim that:
"In 3.0 it is possible. You can enchant the bracers with magic armor special abilities up to +5, as in A&EG. This can be done by using the craft magic armor feat.
The +5 cannot be used for armor bonus just for special abilities.
In 3.5 it is not possible.
However, since there is no 3.5 A&EG, a DM might allow this, even though in the 3.5 DMG there is no such option."
I read the statement emphasized in bold (especially in the context I've underlined) as a declaration that the rule under discussion is something that a ref has to accept when playing under 3.0 rules. That's simply false. A&E is not part of the 3.0 Core Rules. It's just an optional supplement published by WotC. The ref is under no obligation to accept A&E, regardless of the edition of core rules used.
If I've misread you, then please accept my apologies for the confrontation. However, the point about player entitlement is an important one and I don't regret stressing it. Refs have to be able to say, "Not in my game," even when dealing with books carrying the WotC logo. Too often it's assumed that this is illegitimate.