Awarding experience (or DP if you do that directly) can be useful if you need to give your players incentives. Not every group needs that. We level on a "GM says so" basis and all the PCs at once, and it's fine for our group, not to mention much less effort. I can imagine some people would prefer to have a firmer sense of where they are, and the ability to do the things that let them level faster, but it's not necessary for everyone. You want the rules to provide more structure, and then it's easy to ignore if you don't need it.
When I awarded experience, it was on the basis of only three things. 1) Do you have goals? 2) Did you make progress towards those goals? 3) Roleplaying. Those were the things I wanted to reward. It was much less important how the characters made that progress to their goals, because they were the ones figuring out how to do it. I didn't want to give them an incentive to do so via combat vs via stealth vs via persuasion, I wanted them to make those decisions purely on the basis of what was effective and what was appropriate for their characters. It was very important for them to have goals, because I was using that to determine where to go with the story.
You can design an experience system to model learning rather than as an incentive system. RMSS and RM2 leaned more in that direction, whereas RMU is more of an incentive system. I think that modeling learning doesn't work as well for several reasons. One is that it is going to become an incentive system regardless of the designer's intent, and it may give perverse incentives (e.g. rewards for sustaining criticals, or simply for favoring combat over other solutions). Another is that realistic learning is generally slower than the pace of development you want in a game, so realism is already out the window....