Yes. There's drastically reduced availability, and also a sense that the ability, once gained, has been earned. At-will cantrips effectively mean that anyone who has even a passing interest of magic has an infinite supply of it...
No. It means anyone who can use magic has an infinite supply. Traditionally, D&D setting material suggests that you have to study for many years to become a wizard at all. Furthermore, in many settings (e.g., Dragonlance), magic requires an inborn talent which few possess. If you don't have it, no amount of studying will help.
Obviously, 3E-style multi-classing raises a few questions around this, but the assumption is that if you multi-class to wizard, you have the talent and have been studying for a long time, and your studies have finally begun to bear fruit. The XP and level system has never held up to scrutiny very well anyhow.