Some classes get more because they get the "every member will take these, might as well give them out for free" ones.
Rogues get Stealth and Thievery, but they also *need* Acrobatics, Streetwise, Perception and Athletics to do the traditional rogue things (climb walls, walk tightropes, have contacts in the criminal underworld, find and disable traps, etc).
Each class could get 4 skills to train in but differentiate it using some other method - perhaps as a static bonus to class skills or some such.
My point is, I think they could have done something to not make them feel uniform so I would have to think there is some other reason for that.
I'm having a hard time believing that the skill differential is a hold-over from 3e that they simply overlooked. There are too many exacting and fiddly overhauls of the game system to make that a very plausible explanation. I would be open to the differential being a mistaken design decision for a variety of reasons, including other factors that may have been edited out in the final publication, but not simply a holdover.
In a lot of ways (at least to me) 4E is a development form 3.5, and I see no reason why it should not have things that are holdovers form the previous edition. The classes are the same or similar names, skills are similar, why not skill allocations? If it does not hurt 4E or limit it in some way, I can see the value of making decisions based solely on nostalgia. Or largely on nostalgia