Why does your mobile phone have crappy reception when you can see a tower from your window? Every carrier has their own towers and panels. Sometimes they share towers but maintain their own panels on that tower (there are many panels on the average cell phone tower). The tower that graces your bedroom window view might not be *your* carrier's tower.
Besides that, with some phones and carriers, there can be a problem with being TOO close to a tower. I think it happens because the signal is so much stronger than what the phone was expecting that the phone can't use it correctly.
There has also been a push lately for standardization of laptop battery life ratings - those figures need standardization even more severely than cell phone signals do.