That bike is definitely not worth that price but it does indeed look like a 20mm front axle, they use them on downhill mountain bikes, that must be a downhill fork and hub. I dont recognise the brand of fork though. They run 20mm axles to avoid flexing and breakage of axles. The same bikes will usually run an oversized 12mm rear axle.
I have a 20mm axle on my downhill bike as well as my jump/trails MTB, and many MTB hubs are now sold to accept either a 20mm thru axle or a quick release skewer. I have one of these hubs on my Villiers bike and am in the process of changing it to accept a standard solid axle for that "vintage" look.
Heres my hub ready to accept a quick release skewer
Heres the same hub with adaptors removed and you can see how they accept a 20mm axle
Ive often wondered why ive never seen the 20mm thru axle or 12mm rear axle hubs/wheels used on here by some of you race guys. You can get forks in either single or double crown forks to accept a 20mm axle, and they really do make a big difference in the ride quality you get.... ive never considered using them as im more interested in vintage builds.
Heres a single crown setup
http://www.google.com.au/imgres?hl=...tbnw=192&start=21&ndsp=26&ved=1t:429,r:1,s:21