Single player RPGs actually have more dialogue today than the non-fully voiced RPGs of the past. An uncomprehensive list:
The Guinness Book of World Records Champ New Vegas: 65,000 lines of dialogue
The runner-up Skyrim: 60,000
The other runner-up Dragon Age: Origins: 56,000 lines of spoken dialogue, unknown amount of written player responses (Game Informer claims it's over 68,000 total but that can't be right otherwise it'd be the Guinness record holder and they've misstated before, see below)
Fallout 3 and Mass Effect 3: 40,000
Dragon Age II: 38,000
Mass Effect 2: GI said it was 31,000 at first but later on Bioware claimed it was only 25,000
The Witcher 2: 23,000
The Witcher, Mass Effect, Bloodlines: 20,000
Knights of the Old Republic: 15,000. Since KOTOR2 was a shorter game by about two dozen hours or so it probably has less than that.
Dungeon Siege III: 12,000
Meanwhile I've read that Fallout only had about 2000 lines of dialogue.
So maaaaaaaaaaaaaaaaybe it doesn't matter how many lines you're allowed to have, but what you do with them.
Wait, there's no maybe about it.