There are some advantages to specializing and become very good at one format rather than just good at multible formats. But there are lots of players, who win in both tournaments and cash games, both at the highest stakes and online in micro and low stakes games. I have mainly played tournaments including SnGs for the past several years, but I have no problems beating 10NL cash games. 25NL and higher is up for debate, since I dont have enough volume to prove, if I am winning or not.
As others have said you just need to understand the difference betweeen trying to outlast other players and trying to win chips/money. And the difference between playing with a 100BB stack and a 20-40 BB stack, as is more common in tournaments. But even in tournaments you start with around 100BB, unless you late register. So its not like, a good tournament player has no idea, how to play with 100BB. We just dont do it all the time, like cash game players do.