There IS a distinct advantage to having a "magic-user" bucket that you pour wizard, warlock, sorcerer, etc out of: you can tie things to the "magic-user" keyword.
Maybe some magic items can only be attuned by magic-users. Maybe some monsters get bonuses against magic-users. Maybe some items have special properties when used against "magic-users" (sword +1, +2 vs. magic-users? potion of magic-user influence?).
There IS a distinct advantage to having a "magic-user" bucket that you pour wizard, warlock, sorcerer, etc out of: you can tie things to the "magic-user" keyword.
Except that Clerics, Druids, Bards, possibly Paladins are ALSO "magic users". If they all have spells... they all use magic. Now you might then make the distinction between Arcane magic-users, and non-Arcane magic-users... but then we get right back into the Power Source issue that so many people decried.
And what's lame about it is that Warlocks aren't really Arcane anyway. Warlocks are and have always been much closer to Clerics than Wizards... because their magic is granted to them by some much more powerful entity. The only reason they've been called 'arcane' is because there's this nebulous energy called 'arcane energy' that D&D has created and yet has never really defined... and have just randomly assigned certain classes to it. How is the magic granted by a devil the same as the magic you get by using hand gestures, incantations and bit and pieces of random crap? Or the same magic as playing music? To me, they aren't similar at all. So to call a Warlock's magic 'arcane magic' is just hand-waving the fluff because they don't want to call a devil a source of 'divine' magic, since it's always been "the gods" who had a moratorium on that term.
But hell... (pun intended)... Asmodeus is the king of the devils as well as a god in 4E. Which means a cleric and a warlock can get their powers from exactly the same person. If that doesn't mean clerics and warlocks should actually be put in the same category rather than warlocks and wizards, I don't know what would.
Fey pact warlocks... okay, maybe their magic is arcane. Infernal warlocks? Divine magic all the way. Which tells me creating a "super-group" of all arcane casters is kinda useless and is actually antithetical to its own fluff.

(Dungeons & Dragons)
Rulebook featuring "high magic" options, including a host of new spells.