I wasn't goint to but in, since it's sounded like a UK store problem, but I got curiouls and played around a bit anyway.
First, in case we are not looking at the same thing, I was looking at the Music page, Top Charts, and hitting the More button at the bottom of the Top Songs/ Top Albums lists.
The first time I did this I got to 90 songs before the More button disappeard. Before I tried it again I cleared all the apps out of the Multitask bar, to be sure I had maximum RAM. Having doen this I got all through all 100 songs before the More button went on missing.
My tentative conclusion is that you can only display so much before you run out of RAM. It seems unlikely that the iTunes page uses up all the iPad's RAM, but it is possible that if you start iTunes with other apps in RAM, it may not grab as much for it's own use as it could.
The fact that Tim and I with our iPad 2's, and double the RAM, got further than you every time lends credence to that.
My suggestion is that you do like I did and free up the maximum RAM to see if you can get to 100, or at least back to the 70 you had before.
Please let us know. If it does not work I'll have to start working on another theory.