Yes, it would be useful to know this.
My suspicion is that destination rental rates are decided to some extent by renters' residence, so that in markets with high local rates, for example the UK, the companies believe they can get higher returns by charging rates higher than to renters in other markets.
I take this as the 'marketing' you mentioned earlier.
I'd also like to know why I can't get rental-only rates in some markets. I have my own comprehensive rental insurance from American Express UK, which by all accounts is superior to that offered in North America - another market-based offer.
If I book at avis.com or similar websites, I'm typically offered only insurance-inclusive rates.
I always compare, and in the US and Canada have found alternatives which offer rental-only rates and sometimes offer even more miles on AA or elsewhere than the 1,000 VS miles per rental I get with Avis.
As always, YMMV.