buy from online apple store or reseller

No advantage what so ever.
However, some resellers give you hard time on returning your items, so be advised.

The things that I remember are:

The "free printer" rebate. If you purchase from Apple, you get a free printer, up to $100. You pay for the printer, then submit an online rebate and they mail you a check back for $100.

You also have the ability to sign up for a One to One membership only if you buy from Apple.

They also do educational/gov't discounts, as well as discounts for a few big businesses.