Having run a 4E campaign all the way to 30th, I will just say that it gets a little weird after a while. You end up hopping the planes, fighting avatars of demigods. While I had an epic story for the campaign, coming up with such story arcs is difficult.
Think of it this way. At 1st level you're just a nobody. Maybe some locals know who you are and respect you, but that's it. You might deal with leaders of smaller towns but probably not with even a regional leaer. Around 10th level you're getting fairly well known in your region, and meeting with their leaders if you want. By 20th level? At that point your fame (or infamy) has spread far and wide, you may even get into the history books.
So where do you go from there? What kind of threats do you face? You've slain the ancient dragon and crushed the arch-lich. If you go beyond that you're facing foes that could take out small kingdoms single-handedly, and hanging out with the gods. It gets really difficult to have a campaign that's grounded in any sort of reality. So what to do? Your options are limited. You can just move the campaign to some sort of planar campaign where the "orc" equivalent now have hundreds of hit points that can do 150 points of damage per round. You can have a world-ending enemy show up that only the heroes can face.
But it just becomes a treadmill. Instead of dealing with lords and kings, now you're dealing with planar beings. Your campaign loses any sense of being grounded in a standard fantasy world. Encounters that are actually a challenge become more difficult.
That's fine for some campaigns. I had fun with mine ... but it was a once-in-a-decade type of campaign that I would not want to run very often. In addition, after a while the characters and the campaign have a tendency to become stale after a while. As much as I love Grobnar the Barbarian, after a while I start thinking it might be fun to play Pipsaqueak the Halfling Sorcerer.