I have cheerfully built at least 3 par 3's in the last two year that exceed the 250 yard length from the championship tees. What is the USGA gonna' do to me?
The Quarry at Giant's Ridge, Biwabik, MN and the Creek Course at INdian Creek, Carrollton, TX (261 yards each) and Colbert Hills, about 267 yards. I may have another in south Texas coming, but I right now, its only a "measly" 236 yards!
To answer your question, I think those are just guidelines. It is theoretically possible to have a 200 yard par 4, if you determine that, because of a treed dogleg, you couldn't reach the green in one shot. And courses, like Augusta, have exceeded the recommended yardage for years. The tenth was always longer than 13, but also about a mile downhill, so it played shorter.