OS X will see more then 10 access points. It's reporting what it can see clearly and should be able to join. Odds are, if it is a noise issue due to the boosted transmit power, the customers router in question is polluting the channel (and those near it) enough that the MacBook can't see the other access points your other device can. Remember, 802.11b/g works in the 2.4ghz range, where only 3 actual isolated channels exist in the spectrum space allowed. Also, since it's a metal Macbook Pro, they tend to have less range in general then the plastic MacBook or a plastic Windows box. As for setting a preferred access point, thats what the Network system preference is for.


As for never having this sort of problem on a Windows laptop, the issue comes down more to the hardware and antennas. How many customers did you set up with 802.11n cards and MIMO antennas in the laptop? Did you do any checks to see if the connection was actually stable and not having some sort of occasional packet loss/connectivity issue due to the elevated noise?