It is the player getting to control the pace of the bonus to reflect thier interpretation of the character's training rather than the system telling us, you are level x so you have this bonus in these areas that your character never encountered and knows nothing about.
How about the opposite though?
I am a 20th level Wizard (in 3E).
I have traveled continents, been on other planes of existence, battled creatures the likes of which would drive most sane men mad.
But if I walk into a Tavern, my Spot skill is so bad that a 2nd level Assassin can attack me with surprise with ease without me ever seeing him.
I used to have house rules in my 3.5 game that Spot, Sense Motive, and Search (and possibly Listen) automatically got bonuses as the PCs leveled.
Why?
Because after 10 years of adventuring, there are just common everyday skills that every PC in the party would either start learning, or they would die by ambush.
It was ludicrous that someone had to actually "train" a skill and waste skill points to know when someone was bluffing him after talking with 10,000 NPCs over his lifetime. Sure, at first level, the Wizard would be gullible.
By 20th level, this super high intelligence Wizard would have been around the block. He would know many many many things about where creatures hide, how creatures react when lying, etc.
One of the better things about 4E is that as PCs advance in level, they actually get better in all skills because even though we as players do not roleplay and experience every single thing the PC does and observes, the PC should.
And, it's not just about training. It's about experiencing. Noticing how creatures hide behind trees and rocks and not at 20th level be "Yuck, yuck, I've been adventuring for decades, but I still cannot see some tracks on the ground or see the Ogre hiding behind a narrow pole, yuck. I was too stupid to see the tracks of a deer, even with the Ranger pointing them out to me every time we came across them."
Over time, even the dumbest PC would start acquiring "adventuring skills". He would know something about History because the Cleric is constantly telling stories of the old Gods around the campfire, and the Thief is talking about the treasures of the greatest Kings around the campfire.
Using the old 3.5 methods, the PCs are just numbers on a piece of paper. They don't develop and learn in a wide variety of areas as they advance, instead they develop a few set skills and are totally stagnant in everything else.
There are no around the campfire talks in your sterile 3.5. PCs only gain trained abilities, they gain no abilities via exciting lifetimes around the world and planes of existence.
The 20th level 3.5 Fighter knows as much about History as he did at 1st level. Sorry, but that's boring.
PS. A good 4E DM even allows PCs with untrained skills to sometimes use those skills. The 10th level Wizard sees the 2nd level Assassin coming at him in the tavern with his Passive Perception of 17 precisely because he has been around the block and the 30th level Wizard with his Passive Insight of 27 even knows the instant that he walks through the door that it is an Assassin, just by the way that the Assassin is carrying himself.