I have asked the same question last week.
Yes 225/35/19 is a more correct diameter than 235/35/19.
It's just everyone around here is obsessed with bigger and wider
235/35 is almost a half an inch taller than 225/35, that's why everyone seems to look jacked up when they put it on like that and then end up dropping/lowering the car.
By the way, I have been meaning to ask the poster above:
***OEM BMW TPMS****(SPECIAL $246/set) - how is that a special when they're 190 or so on tirerack? Just curious http://www.tirerack.com/wheels/TPMSS...=Sport+Package