Oklahoma State alum here. Registered when it looked like y'all were going after Gundy. My first post.
The spread does NOT need a mobile QB. Look at Brandon Weeden last year for OSU. He was anything but moble. Accurate passer-YES. Rocket arm-Yes. But mobile-not hardly.
Can it be run better with a mobile QB-Yes. But if you have a very good RB then you can rely on an accurate passer and march down the field.
What makes the spread work is a QB that can release the ball fast and get it to a speedy WR or Slot Receiver. Example: Last year for OSU....Weeden to Justin Blackman.
The other thing that works for the spread is the alignment of the O-line. Where with the I or Power formations you see the O-lineman's feet within a few inches of each other and subsequently the D-linemen will head up on these folks and bingo you have a crowded interior. With the spread you often see O-linemen that will line up as far as 3 feet from each other. This makes the D-linemen have to head up on them or run the risk of getting blocked down (away) from a sweep or off-tackle play. Plus it makes the D-linemen have to run further (read: be further away) to get to the QB.
I personally think that the Spread could and should work well in the SEC. With the right folks in place it can be a very explosive offense. The problem with us (in the Big 12) is that our defense's have to try and stop that. When you have the right combination (ie. Weeden-Blackman last year) the D gets run ragged.
Oh, and for what it is worth, if you think it is pass only: OSU has had the top Running Back in the Big 12 for the last 6 years straight.....and all of them with over 1000 yds each year.