Fight Night Round 4's next DLC delivers four fighters, rivalry matchups, and "old-school rules," which I assume means a brain-pulping 15 rounds. Its next patch release will tire the hell out of your boxer if you don't fight smart.
Continuous punching, weaving and haymakers all have higher endurance cost, spamming your block ruins your ability to perform a perfect block, and no nutshots can be thrown if one user is in a stun state, both eliminating cheap knockdowns (and cheaper recoveries).
You can see the full list at the end of this video. The patch (free) and the DLC (800 Microsoft points/$9.99) are out in early December.