I think it is a very reasonably priced feature. It also generates revenue for Yahoo fantasy games thus slowing the pregression to a full-pay site.
I consider myself quite a bit more than just a 'casual' fantasy baseball player. I'm not buying Stat Tracker simply because I really don't feel I have a need for it. I can find out how my players are doing thru other sources. I'm in no rush to see the standings update minute by minute. It's only $10, but I'm not going to buy something I really don't feel a need for, no matter how reasonably priced it is.
I do appreciate Yahoo's philosophy of 'pay for the extras' though. It allows the rest of us to play for free. If you want a little extra, you can plop down $10 for Stat Tracker. If you want even more, you can join up for the Plus service.
* Steroid induced record