Without getting too much into the politics of it but since their inception the Saudi's have been an ally of this country (in fact the British Empire helped create the new state with violence might I add)
That arrangement suits the house of Saud and it very much suits Britain and the west, that relationship isn't changing. Russia hasn't been an ally so that comparison doesn't work.
Also, the fact that the hijackers of the planes were all Saudis yet it's Afghanistan that got bombed to smithereens whilst Saudi was untouched should tell you all you need to know about their relationship with the west