Difference between messenger and laptop messenger bags

Is the classic ballistic messenger the same as the laptop messenger but without the laptop compartment? In other words are they the exact same dimensions?

http://www.timbuk2.com/tb2/products/m...
http://www.timbuk2.com/tb2/products/m...

If so you should be bale to fit a computer of the size indicated in the laptop bag also in the ballistic messenger, right? If I go a classic large classic sleeve, will it fit in the medium ballistic messenger?