There are several threads with information about this sort of thing, kaikara. My basic understanding is that when the Touch was first released, how the readers "partnered" with other sellers (for example, Borders in the US vs Whitecoulls in NZ) accounts for some of this. The base firmware on the device when purchased may also influence this.
Kobo has not yet (and may never) weigh in on installing from the .zip file. They did tell people NOT to install the 2.1.1 .zip in a thread all its own.