Sorry, I don't buy either reasons
1. If it is to serve as an indication of quantity left, I put it to you that the Espace arrangement is superior, in that it worked (in the absence of a real, Honest-To-Goodness gauge or light on the dash)- A black ribbed tube which S-C-R-A-P-E-S as you pull it out will give a useless indication, unclear to boot!
2. Breather tube? Then the hole in the cap is all that's necessary, shurely
Either way, poor design at best, unnecessary at worst (especially when the first filler bit falls off and you have to wedge it back in place, and no matter how you jiggle it, it still leaks screenwash on the forecourt
)
Maxbert