My friend Mark is a really good windsurfer. He used to be just kind of good, but he moved to Florida and sails all the time and now he's really good. But when he and I windsurfed together, he was infatuated with wave sailing. The problem is, you only get to really wave sail a couple of times a year (at most) in Rhode Island. It's windy enough here that you get to sail a lot, it's just not that often that wind from the right direction coincides with good waves - and it's not a Wednesday afternoon and you're stuck at work, or 26 degrees out. Newport ain't Maui.
So Mark had a bunch of equipment that was geared quite hard toward the wave sailing that he so enjoyed and wanted to do all the time, but never really got to do. The issue was that when conditions were great for the sailing that you actually get to do quite a lot of here, his gear was marginal at best. So he spent a lot of time on the beach frustrated, when if he'd accepted that Newport ain't Maui and had more appropriate gear, he could have spent a lot more time enjoying the good conditions that we do get.
What does this have to do with anything?
23mm tires were the new 21, then 25s became the new 23s, then 28s, now we've kind of jumped straight over that and "real" tire clearance is for, like, the better part of 40mm. The problem with that is that you're dragging around a lot of compromises full time if you've got clearance for tires that big but don't actually do the kind of riding that calls for them.
I recently read a forum thread where a guy was bemoaning the lack of tire clearance on his race bike. The bike in question is a good one, very much a top level race bike. The prevalent thought was that any race bike worth its salt should be able to fit "any" 28 with no problems, a thought with which I can't agree. A top end race bike needs to be a lot of things - stiff, light, fast, hopefully not a dog in the wind, stable, nimble, ergonimically correct for the "chew on the bars and kill yourself" position that we do whilst road racing, and some I've probably missed. Excessive tire clearance is at odd with at least a few of those - wheelbase has to get long, axle to crown on the fork has to increase, chainstays need to be wider which drives a whole lot of other factors, if you make the BB height correct for say 30mm tires, then it's going to be pretty f-ing low with 23s on it, and the bike is going to weigh more, too. Plus the fact that when we talk about "any" 28 on any rim, we're really talking about 31 to 32mm tires. And please please please please we need to stop bringing in pro tire choices when we have these discussions - pros ride tubulars which are pretty close to the size that they claim to be. The 25mm clinchers that you have on your road bike are probably substantively bigger than the 27s that pros sometimes ride, and way much bigger than the 25s that they often ride (not to mention HUGE compared to the 23s that they also often ride).
This isn't an argument against Swiss Army, do it all, one bike solution bikes. Not at all. That's a perfectly valid bike. I just don't want to race the crit at Green Mountain Stage Race on it. Or any other crit. Or most road races. Some group rides, sure fine. This is, rather, a "can we please let race bikes be race bikes?" question.
I freaking love riding nice race bikes. It's awesome.