I assume its because he's had a new voice actor since that PSP game.
The main reason I prefer it is because Altair's voice felt so horribly out-of-place in AC1. It didn't feel "gruff no-nonsense" so much as it sound like "guy from the 21st century interacting with guys from the 11th." It's part of the reason why I liked Ezio so much. He actually felt like he fit in voice-wise.
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TheRock ~ Death By Misadventure, Not Suicide
"Would've liked to see that." - Ayuyu on my boner