In 4e a level 1 lock is simply not intended to be a challenge to a level 20 PC of ANY class. It will never appear in-game in the context of being such a challenge. Thus there is no issue at all. Tasks become harder for high level PCs because the things they face are literally more difficult. The 20th level wizard will NEVER ENCOUNTER a level 1 lock as a challenge.
I want to point out that this means the 4e skill system is strongly designed for a specific gamestyle (or at least, a specific style of using skills and related challenges in your game).
If you want that gamestyle the system is perfect. If you don't want that gamestyle the system is a failure.
I don't think it's easy to create rules that are so flexible to allow many gamestyles of course, but I'm just saying here that it's a moot point to argue about how great a (sub)system is when other people are looking for a completely different style of handling this part of the game.
In this case, I want a level 1 lock to be always a challenge to any PC who's never ever bothered learning how to pick locks, no matter if she's a 20 level PC. And if nobody in the party ever bothered, then I want the whole party to be challenged by that 1st level lock (if they try to pick it, obviously if they're level 20 they most likely have alternative ways to deal with the lock!). That's part of my favourite gamestyle regarding to using skills.