AlphaFoxtrot,
Well, with UK.COM, Centralnic's holding of UK.COM itself is subject to ICANN guidelines.
However the process of issuing subdomains under UK.COM is subject to whatever commercial and legal terms that Centralnic dreams up.
This means, for example, that you don't have access, for example, to ICANN's established dispute resolution policy (e.g. used if you fall into trademark rights issues on your choice of name).
Some might also argue that UK.COM names are somewhat overpriced given that for a predominantly automated process where no fees are due to higher level entities such as ICANN, the RRP is £32.50/year.
Is it something like if you buy a sub-level and there's an issue...can a site simply be wiped from existance rather than buying a .com/ .uk site where it cannot?
Well, I'm sure some investor would happily snap up what Centralnic left behind in the event that anything happen to them. I guess you could speculate it might not be as much of a tidy transition.