App updates showing on iPad/iPhone but not iTunes - why?

Hi Guys

My iPad / iPhone keeps showing I have app updates, but when I go into iTunes and check App Updates it says non are availble.

Its not ALL apps, but just a few.

For example, this app is ready to update on my iPhone but not on iTunes http://itunes.apple.com/gb/app/drag-racing-free/id470867961?mt=8

I have just updated 4 apps via iTunes, but iTunes didnt see this app was ready to update, but my iPhone is.