Dear alexniedra

I agree that the optics on the the 17-55 are quite compareable. But the 24-70 will allway out perform the 17-55 let's just compare
The 24-70 is all metal, weather sealed, L series and fits all bodies including film.






As for the 17-55
Its plastic, not weather sealed It collects dust horribly!!, and only fits on the digital rebel and xxD series bodies


So let's think the only benifit of the 17-55 is the image stabilzer which is useless on a landscape lens cause you would use a tripod for that and the other is the price is cheaper
But in this case unless you are broke or just well d*#b t here is only one real choice that is the 24-70mm

Hope this gives you some insight into why canon makes L series lenses

Coastal kid88