> What's stopping me from buying them all up at the Apple store and selling them to overseas customers?

Import duties and VAT. VAT accounts for much of the price difference, OP didn't explain which Europe they're talking about, but assuming a 20% VAT a 2999 machine costs $3598.8 to the end-user.

Means you're working with a 325.2 price difference, which doesn't even cover import duties.

So pretty much as ever, if you're round-tripping through the US, picking up an MBP there is nice. It does not however make for a business.