Why are there still so many Trojan infections?

I just scanned the Eset, Avira and Kaspersky forums and do not see the rash of Trojan infections I see here.  I'm surprised they are still so prevelant.

 

This begs the question as to whether there is something inherently less secure about Norton when it comes to Trojans as compared to these products.

 

I can assume outdated signatures is a common issue across products, so I can't lay the blame there.

 

Is it because Norton has a much bigger market share, or it is detecting them when other products don't?

 

Will the 2013 products do better?