You need to be able to report to your base (in this case, LGW) within 90 minutes if you are on Home Standby. In theory, you are meant to be within 90 minutes from base but in practice they don't mind if you live further away so long as you can fulfill your standby obligations. They also specifiy 90 mins because of issues such as training and meetings where you are needed on base. People who do live away may complain about having to make a trip for, say a one day manual handling course, or a one-hour meeting. The company can come back with "you are meant to live local, it's not our fault if you live away".
Plenty of crew commute. For standbys, they just stay with friends, at BnBs or even drive to a Motorway services centre 90 mins away from LGW and sit around all day with their mobile.