20-mins delayed stock quotes are a comodity right now, and pretty cheap. it is the real-time quotes, (the one that every investor needs), that have been expensive.

There is also Level II quotes, with wich you can see trades going on in real time, but these are even more expensive, and brokers will only give them to active trader.

The whole system, is rigged in such a way, that if you are a casual investor, you have a lot less information on what's going on, then people that have these tools available. What Yahoo is doing, is actually pretty game changing, and makes a comodity something that was only available at a premium.