The US and NATO casualties are less not due to the weakness of Talibans, its because of the fact that they are relying on air in most of the cases and avoid road movements as much as they can and where there is a real need, they keep Afghan Army and Police on the front. But you must remember, you can't rely on air operations entirely for an idefinite period, which leads you to resort to road movements, including logistics, which remains a sour point for the US and NATO. See how many logistic convoys have been attacked and destroyed by Talibans.
Regarding Taliban's casualties, I agree, but not in numbers, as being portrayed in the western media, while they try to conceal their own casualties. You see, mainstream media is in their hands, whatever they feed to the people, will be taken as true by the majority.
Talibans have gained momentum due to their recent resurgence and they are unlikely to be defeated, till they enjoy majority support. People consider them as real warriors, who have been resisting foreign forces for years and haven't surrendered, despite being negligible in strength and resources. Its something to do with ideology, faith and conviction, which drives a smaller force to remain steadfast and face odds and critical situations cheerfully.
I again disagree that the US and NATO are getting effective against Talibans. See yourself, the US has been complaining regarding NATO's role in the war. I happened to scan an article yesterday, where Americans have alleged NATO for not taking due interest in active operations. Any person having a balanced and unbiased thinking can reach to the conclusion that the situation for the invaders is not as rosy as being depicted.
A couple of months back, I read an article in Newsweek, in which it was claimed that the Americans have enhanced their budget against IEDs (improvised explosive devices) from US 4$ to US 6$ for the current year, but the chances of getting any significant success aren't much. They expressed their utter dissatisfaction over destruction of their million dollor expensive equipment being destroyed by these cheap devices having worth no more than a pizza.
Just analyse, a strong US and NATO force, equipped with latest systems and 100,000 Pakistani soldiers deployed along the border, carrying out operations, but remain miles behind of any visible success. The credit goes to Talibans.