Yeah, it's part of the new "negotiation" system used for GTS negotiations. No 3 for 3 trades. :(
There are several annoying aspects about G5 (no pots like in HG/SS is just one) - some of them can be fixed in this generation's "Platinum" if they wanted to. Others... we're stuck with.
Personally I like 3 on 3 battles, but I think rotation battles might be due a "contest/pokeathelon" ommision from the next gen.