It does have to do with the evolution of the XX4. Very early cars did in fact have only 2 rows of holes, 2 on top and 3 on bottom for 5 in total. Check an early Matt Francis set-up sheet here to see:
http://www.losi.com/Content/PDF/Setups/xx4/xx40001.pdf
Losi quickly changed to a beefier tower - even before the WE came out, as the original towers snapped very quickly - and they added more camber link holes as well. For reasons I'll never understand, they didn't redo the numbering system for all the new holes. The hole that got added to the outside top row was numbered 2.5, so that the inner three holes of the now middle row stayed 3, 4 and 5. The outer hole added to this middle row was labeled 5.5, and then the three on the "new" bottom row were numbered 6, 7, and 8. There's a very inner hole on this new bottom row that's not actually usable, I don't believe, so it was not numbered. That's how 11 holes have 8 numbers: one isn't used and there are two "half holes." You can see this numbering scheme on the XX4 WE blank set-up sheet, here:
http://www.losi.com/Content/PDF/Setu...we/xx4we00.pdf