Does anyone else see that we as contributors are at least partly to blame for this?

123RF gives us a very fair commission of 50%, they perform pretty well for us, and in the meantime new agencies pop up offering lower commissions and prices and we stand in line to join. 

It's the Fotolia story all over again.  How can we expect the larger players that sell at higher prices and offer decent commissions to maintain those prices and commissions if we keep adding to the "race to the bottom" pressure?  It's simple economics, and we're a big part of the equation.

Prices are not the only thing that drives customers to your site. You need a good reputation, a good company image, something unique to sell and please your customers. That is difficult, but not impossible. If you can't do that, despite good prices, customers will leave. If you can't compete in the world of microstock (as an agency), then you're doing something wrong, and it's not the contributors who are to blame. 

Lowering commissions is simply a move of desperation.

That being said, it would be good for us contributors to not join the cheapest agencies, or sell yourself cheap, but there are so many individual contributors that it's impossible to direct them. It's the way the market works, and to maximize your profit, it's best to play along.