upstairs taps?

hi , i have was wondering why the upstairs cold taps and toilets are not mains pressure they are fed by the big tank in the loft, i can understand the tank feeding the hot water cylinder for the hot taps, but why are the toilets and cold fed by the tank rather than mains pressure. all my cod taps, toilets ,ect downstairs are mains pressure.

i have pump showers upstair which are great and effective no problem there, just the toilets take some time to refill funnily enough cold tap pressure which is fed by the tank seem to better than every other cold tap upstairs, anyway cheers