No MATTER how you want to argue it, a 45' coach will not fit in every campground. Your County, State and National parks were not built for 45' coaches. Many of those parks do have several spots where a 45' will fit only because those particular sites had some extra overhang space or they cleared some spots when they could.
We've been traveling throughout the west for 40 years and a few times back east. The NORM is not to have 45' sites unless it's a private campground/resort or possibly one built in the last couple of years.
Sure, with a little work, you can plan ahead and find a 45' site, but you certainly aren't going to drive down the road and just pop into any campground and find a site that fits. When we had our 36' coach, we rarely found a park that couldn't fit us, even at the end of a travel day, without reservations. Now, with a 40' coach, it requires more planning to find a place that we'll fit. Remember, many people on here driving 45' coaches are full timers, know what parks they'll fit in and often stay at private campgrounds a little father away from their intended destination. A perfect example of this is Yellowstone. Their max limit at the interior campground (Fishing Bridge) is 40'. There is really no wiggle room there. I know that many with larger coaches like to stay at Grizzly, a private campground, on the west side. It's a nice campground, but requires you do a lot more driving in your toad.
This is not a put down of larger coaches, I personally wouldn't mind have a 45' with a 600 HP engine, but the reality is they require you to camp a little differently than coaches 36' and under. Typically, those driving that large of a coach are not wandering from County to County park, but driving to destinations and staying a little longer.