I thought that too, this is from Surly's website - Each Straggler frame (650b and 700c) was designed for one wheel size only, so we do not recommend a 700c wheel for use with the 650b frame.
there's another comment which says the same for a 700c frame with 650b wheels - no idea why this is the case.
It'll be to do with the clearance. 650bx48c in 700c frame was a little close in some positions along the drop out. Nothing a bit of dimpling couldn't solve. Will dig out a photo later.
Don't think they make 650b frames in the larger sizes, if they do the distributor doesn't bring them in.
I thought that too, this is from Surly's website - Each Straggler frame (650b and 700c) was designed for one wheel size only, so we do not recommend a 700c wheel for use with the 650b frame.
there's another comment which says the same for a 700c frame with 650b wheels - no idea why this is the case.