Got my copies of Windows 7 Home Premium retail for £39 and £44 on pre-order

I don't understand MS's pricing tbh - I'd happily pay £70 for home retail but no way I'd pay that for OEM - when the pre-order was on several people I know bought copies that have never paid for MS products in their life - one guy I know bought around 10 copies for his PC setup at the pre-order prices when in the past he always pirated all his previous OS (mind you I think he flogged 5 copies later on to make back most of what he spent).
Previously to getting Win 7 pro retail, I had Win Vista OEM. Everytime I changed a component I had to ring up the automated service to activate it again which was far too annoying. I actually managed to reactivate it on new mobos and hard drives, just pick the right answers to the questions and it gets reactivated, easy.
Prior to vista I never had a single legal version of Windows - I had all my OSes provided to me by friends / relatives, and lets say that they were all huge fans of getting software for free rather than paying the ridiculous prices that MS charge.
Yeah no way I'm paying £70 for an OEM license tied to one PC... £30 maybe.
The OEMs can actually be reactivated using the automated service, they dont actually define what they mean by 'Is it being reinstalled on the same PC you got it with' when the question is asked ... hmmm, new motherboard and hard drive, same everything else, ok that to me means yes, its being installed on the same PC ...
'Thank you, here is your reactivation code'.
How is this actually detected? E.g if you upgrade your motherboard, would MS know?
The OS detects the new components somehow, and says it will deactivate after a certain amount of time without a reactivation code, which you get from a free to call automated service.
With the retail versions though, you simply pop in whatever new hardware you want and it carries on working, it is a lot better than the crappy OEM versions if you upgrade your components.