Is purchasing a valve necessary when shopping for a bathroom faucet?
The first product is a 3 finish piece faucet and in this case Moen has turn it into a feature where you can just swap out the 3 finishing pieces without touching the underlying valve.  You need to buy the valve separately and it is specific to that series of three piece faucet.

The second link you have is a single piece faucet that has everything in it.