Interesting!! Although i cant say why, ive had similar with my laptop.
Before we moved recently, i discoverd that my next door but one neighbour, who was two driveways, and one complete house away, had unsecure internet - so i cheekily, and probably illegaly, did some sneaky tests with my own internet v his and discoverd that with my laptop sat next to my own router, using my internet, the signal varied between 100% as expected, and 70-80% if i moved around the house. Yet using my next door but one neighbours internet, i got a signal of always over 65%, and in one certain room, sometimes over 70%, and discoverd i could download at over 70-100kpbs!! Not bad considering the distance i thought!
Talking to him revealed it was indeed NTL/Virgin he was using, as i was.
Now ive got BT broadband, and although the hub is connected direct to m main PC, ive faffed with the wireless on my laptop and with the hub downstairs i can barely get 70% signal upstairs, although line of sight gives me 100% with the same speed i get on my main PC....although even though it says its connected at some silly fast speed, thats only the link between the hub and the laptop, sadly

BT sucks, so far!