More what? I makes since that balance is harder and more group dependent higher level the characters are. The GM has to counter for the group. What would you do to counter for later game access to an increasing number of magical equipment items, increase funds, more spells, and more class abilities that open a huge number of play possibilities based on group selection and individual player choices if you have no idea what those choices are or if the opted to homebrew and without knowing what optional rules like feats they are using? The more freedom and tools the games gives the harder for the designers to hope to balance it. Its so much more than an MMO like WOW the balance comparison is not relevant.
I think there are tiers of this. Its true that balance is more difficult at higher levels. That said, even if you take a regular old "balanced" party of the core roles (fighter, wizard, cleric, rogue) and go into high level fights you can quickly see that the standard CR encounters don't cut the mustard. The monsters generally just don't do enough damage, and can't take enough damage, to remain a threat. Further, part of the problem is that abilities just scale up...but to challenge high level parties you need more "epic" abilities to really do the challenge justice. Dragons are probably the worst offender here. High CR dragons are just the same as lower dragons but with higher numbers. They don't get anything new and unique to deal with the power of high level threats.
One example from 4e that I used for high level games.
1) Low levels: I used the standard "ongoing damage". Example: Take 10 fire damage. Make a save. If you fail, take 10 fire damage again next round. Rinse and repeat. This was a normal 4e ability.
2) Mid Levels: I introduced "escalating damage". Example: Take 10 fire damage. Make a save. If you fail, take 20 fire damage next round. The round after that, take 30.
3) High level: I introduced "crisis damage". Example: Take 10 fire damage. Make a save. If you fail, IMMEDIATELY take 20 fire damage. Continue making saves until you pass or your dead.
Its not just higher damage, but the frequency increased to match the power of high level opponents. And let me tell you, that crisis damage scared my high level players!