I totally agree with the comment about how niche sites "should be" marketed and how to retain members for a good biz plan.
That said, I also think that the larger sponsors that have 40 or 50 "niche" sites that sometimes include access to the same members area or offer access to 10 other sites as well, do so not to fill the niche, but to get cross-sales and their own sponsor/inside sales. A large sponsor that does that can make a profit based on those cross sales and email collection etc, and really have very little concern with retention.
Add to that the fact that a large sponsor is going to have hosted galleries/other promotional products that will get used by hundreds if not thousands of affiliates, with loads of crappy traffic but keeps the sales ratio high enough that it doesnt really matter if the surfer stays on for more than 1 extra month. That is all figured into the profit margin (which is very low for these sponsors - a good indicator is when they are worried about chargebacks in the micro percentages)
and as long as they stay above a certain percentage it doesnt matter what the niche is as long as they fill TGP and LL categories with their banners/links.
Add to that the recent explosion in sponsors getting into the SE game by using rather shady practices to get traffic and you have a perfect recipe for their ability to convert just enough niche traffic to justify having a tour built for that niche no matter what it says.
For the purists in us (I have a niche that I know damn well) there will always be much better converting and retaining niche sites that know what they are doing and we try to help build the brand name to help educate the surfer - and that tends to give us an extremely good return in the end and eventually the big sponsors tend to drop those niches (has happened twice in the last 1 1/2 years that I can remember) as the very low conversion ratio doesnt hit their profit margin anymore.
Just my opinion
