I travel full time, and have been living all over the world for the past four years and never had this problem. From Romania to Chile, Venice to England wherever I am, my iTunes works the way I'd expect.
Compared to HULU and Netflix, Apple is one of the best in this regard. I have to get on a VPN to the USA to use my HULU or Netflix accounts, but iTunes just works, globally.
I have a US itunes account, and use it in whatever country I am in with no problem. Apple has never checked my IP address (so I think that's speculation on his part, or a mistake on the part of the support person he talked to.)
It doesn't make sense to have multiple iTunes accounts, and it would be good if Apple would let your merge them.
But it isn't Apple that is making them tied to regions, this is a requirement of the record and movie industries who seem to think that price and release discrimination by region makes sense.
In fact the only time I've had any problems as in Mexico where iTunes Match wasn't working (though Apple has rolled it out there now) but that was likely due to low quality internet, because here in Chile, with no iTunes match, my US iTunes Match is working fine (but a great internet connection.)