ability to play as pure magic user would rock!

[Ryastar]

I think the thing here is that those spells you mentioned, spells that don't scale with int, are ones that are meant for warriors and paladins, whose intellect is lower. I agree that their duration should increase as advertised though. It must be either a glitch or an oversight, because i see no stated reason anywhere why every 15 int doesn't increase the duration of those spells.