Almost everything that establishes character capability and progession in D&D is determined by a rule/formula. The only exceptions are a) some methods of generating ability scores and b) generating hit points. You don't roll to see how many skill points you get. You don't roll to see when you'll get another feat. You certainly don't roll to see how many XP it will take to get to the next level or how many spells a 4th level cleric can cast.

Rolling dice adds a random element of risk to performing any action. The player knows what his or her PC's skills are, the DM gives an indication of difficulty, and the player has to decide what to do. It's a gamble. This is what makes the decisions meaningful and important.

Bob the fighter is dying near the edge of a courtyard. Frank the bard only has 4 ranks in Hide and Move Silently. Can he sneak past the ogres to save Bob? If he blows it, he'll be caught, too. But if he doesn't get to Bob, in the next few rounds, Bob will probably die. Frank could have learned invisibility last level, but darn, he learned another spell instead. He could cast ventriloquism to distract the ogres, but then he won't be able to cast expeditious retreat if he needs to escape quickly. Frank's success or failure relies partially on die rolls, but his player and character choices have a lot more to do with it.

Rolling for character attributes doesn't involve any element of choice or risk. You have a choice of where to place the stats after the fact, but it's not something you can opt to do or "gamble" on. The same goes for hit points. When you advance a level, you're going to roll hit points. Because of this, I don't think either should be rolled. Rolling for such long-term effects does not reward or penalize player skill or choice in any way, it simply rewards and penalizes dumb luck.​