I imagine they want to screen everyone's FEX-W to save themselves hassle down the road.
From what I've heard they have had a few guys do what they were warned against doing in other threads, ie saying they had a FEX-W before they actually did. This was done by saying they had one, when in fact they hadn't taken the exam yet. (This was done on the initial Profile page where you verify you have all the minimum requirements they want. Clicking the button before you have a current FEW-W is tantamount to lying in FedEx's eyes. It is verified by date one applies and date on FEX-W. )
Rumor has it there have been some that have gotten the boot for doing this; some even got as far as doing the paperwork after getting conditional offer and this was discovered and they were sent packing!
Moral of the story. Don't say you have things if you don't! Sounds simple but apparently a few folks don't do it.