framer, who decides the runway? - the tower and flow between them. How? - not in any particular order - noise abatement, wind, "mode" (as in more departures or more arrivals).
I say this in all seriousness - if you're unhappy with the assigned runway then utter the words "require" and you shall receive without question. We aren't on the flight deck with you so don't know how rested or otherwise you are, what other factors there are and what you feel comfortable with handling at the time. For all we know you're on your first leg so have only been in the air for 2 or 3 hours and feel fresh as a daisy.
SP, external factors such as wind - the stronger the headwind the slower your ground speed is down final and the more time we need to keep distance standards, whether we're on instrument or visual approaches, single or two runway ops, as has already been highlighted the availability of high speed taxiways, whether we're in departures or arrival mode.
Answering your other questions:
a) we work with the rules we're given. I was under the impression that similar speed restrictions apply at many places overseas.
b) we've been told you guys will ask if you want it and not to offer. That said if I see a big gap I'll shorten you up and ask the flow about cancelling speed (I work en-route and arrivals).