"Instead of the fighter getting a better and better attack bonus, he instead gets more options to do stuff as he goes up in level, and his attack bonus goes up at a very modest rate. I think it offers a better play experience that the orc/ogre can remain in the campaign, and people can know how the monster would work from a previous experience, but they remain a challenge for longer." - Monte CookSo let's talk about scaling bonuses - Warning, this is about to get mathy. Let's say you're trying to pick monsters for a fun and challenging fight in a 4e campaign. A monster becomes too powerful to use in a fight when its AC and other defenses are high enough that PCs need to roll very high (natural 17+, I'd say) to hit. There's also a band, which I'll arbitrarily identify as requiring natural rolls of 13-16, where the game might be fair, but it's mostly frustrating. For comparison, I'll note that we're talking about ACs of 19 to 23 to challenge 1st-level characters. Based on the Monster Statistics By Role chart on p. 184 of the DMG, this represents 3rd to 7th level for soldiers, or 7th to 11th level for brutes and artillery.
Is this a valid way to judge what you should use to challenge the party? Not remotely, but the point I want to make is that 4th edition paid a lot of attention to likelihood of hitting an opponent, and scaling AC and defense out of reach is a primary way of signifying that an opponent is too tough for you right now. The same is true, of course, of low-level monsters threatening the PCs; once they need high rolls to hit the PCs' defenses, they should really just pack it in unless they are there to slow down the PCs while a boss of some kind does the actual damage.
You reach a point, though, where it just doesn't matter how many low-level monsters you throw out there, because hitting only on 20s is not a valid threat. PCs reach the point of sneering at orcs, even dozens of orcs; a little later, they can sneer at dozens of ogres, and so on. Obviously, you always have the option of creating a new stat block that is a higher-level orc - that's entirely beside the point. You've outleveled orcs as a threat. The same thing happened in a different way, at a different time, in 3.x D&D. We regarded it, in both editions, as the natural order of things; in heroic fantasy, should the high-level champions of the realm be threatened by orcs?
5e seems to be saying, "Yes, you should still have to worry about orcs, at least in very large numbers." Orcs and ogres "remain in the campaign;" they're saying (I presume) that you could have an epic war against the orcs, because orcs don't (or don't quickly - we'll see how the math plays out) reach the point of averaging near-zero damage per round against the party's fighters.