Zavvi is the new name for Virgin Music. Zavvi have taken over all the Virgin stores and the online side of that business.
Wii Fit has been very popular with Wii owners and subsequently has been hard to source. Zavvi are pretty good, I've had a few orders with them, but sometimes it has taken a little while to source certain items. You will get your item in the end, but for the reasons outlined above, it looks as if they are having a problem getting hold of it for you as quickly as they had hoped.
If you are still concerned, email their customer services. I'm sure they will set your mind at rest.
As a side note, Zavvi started a mega-sale yesterday and attracted so much traffic that it crashed their site!!
