I agree with you - I've been to Syria many times over a ten year period (I'm a travel writer and co-wrote two editions of Lonely Planet's Syria and Lebanon guide) and I've never come across filth comparable to that which exists in the top 10 cities.

What disappoints me more than the pollution in poverty-stricken/developing cities is seeing filth in wealthy Western European countries. I've just spent 2 months in Cyprus and Crete and while they certainly have beautiful landscapes and some pristine beaches, the amount of litter and junk to be found scattered all over both countries is appalling, as is the fact that you're guaranteed to see informal 'garbage dumps' outside every town and village, i.e. a place where the locals have just decided to dump their trash and unwanted stuff (rusty fridges typically found here). Seeing this waste piling up in a beautiful field or sliding down a lovely mountain is disgusting. (I've recently posted about this on my blog: http://cooltravelguide.blogspot.com.) I don't know what others think...