Why do people bring up Twin Strike when the Scout's Dual Weapon Attack is just as bad?
Well, likely because Twin Strike is the 'classic' problem power, and is more common. And, arguably, worse in most situations - the Scout's Dual Weapon Attack requires the first attack to hit. With Twin Strike, you are always guaranteed both attacks.
For a character who has supremely stacked both attack and damage bonuses - which the Scout can do - Dual Weapon Attack generally comes out ahead. But with Twin Strike, even a moderate amount of optimization starts to be problematic... and the Ranger comes with all manner of other double attacks and free attacks which can make the issue worse. The Scout doesn't quite get into such territory (and, instead, can stack up on charging bonuses and that area of issues.)
Anyway, I don't think anyone is saying Twin Strike is the only example of this issue - it just happens to be the poster child for it.