It actually isn't a limit, just a guideline and isn't applicable to AMA members.

It isn't restrictive at all. In an hour, I'll be out at one of the 3 AMA registered club fields around here flying my Extra 330 and a 2meter glider. The Extra will be doing competition maneuvers and probably top out around 450'. The maneuver floor is maybe 150' I'd guess. Don't have an altimeter in the Extra. The glider will top out wherever the lift and visibility decide. Both planes have my AMA number on them and my membership has been since the 50s. Oh yeah, the vario/altimeter that's temporarily in my glider usually shows 350-450' at the TOC when I start hunting thermals. It's pretty near the usual launch zoom when flying pure gliders off my highstart.

However, this year the 2m hasn't gone higher than about 600' and today's forecast doesn't suggest any conditions that promise beating that. The field where I'm going today is in an area where a fairly large flight school brings students. We often hear their engines chopped to idle and watch them experience or practice stalls. That field happens to back on a ridgeline that's 250 or so above our runway. And just north of us is a 2,400 "hazard to navigation". (we're at 860') It is quite a pleasant view that way. Maybe that's why the school comes this way to "work". BTW, I'm not suggesting the altitude hazards around our field have any applicability to our models.

This is real life, and that 400 certainly is not restrictive, as it really doesn't apply except as a guideline that is invalidated by a number of things.