Boilers in bedrooms...?

[MontyVeda]

Why do a lot of houses with a downstairs bathroom have the boiler in one of the upstairs bedrooms?

Is it to get better pressure in the pipes?
Is it because it's the easiest outside wall to install it on?

Surely in the bathroom would be a more obvious place... but is that even allowed?

 

[Electric_Andy]

It might be that, historically the water tank was in the loft which collected rain water, and then had was close to the boiler perhaps? My old house had the boiler in the loft but no water tank. Also my current house has a (retrofitted) downstairs loo and the boiler is outside right next to it

 

[presta]

Both my boilers have been in the kitchen, same place as the multipoints before them. Why would anyone want the noise of a boiler in the bedroom?