To be fair, by the end, Sky were showing Buffy and Angel just a week after the US. (Although Sky's record with Buffy was a bit iffy, deciding to drop it half way through season 2 to show Third Rock from the Sun, which turned out to have lower ratings for Sky than Buffy did.)
And also it appears UK TV companies get complaints if they show shows just after the US showing because of the large number of gaps the US TV companies fill with repeats. 22 episodes in the average US season, but shown in the US over about 40 weeks.
The old system from those days, where a US show would appear on satellite and then appear a year or two later on terrestrial, seems to have disappeared. Presumably because of the large number of channels available on Freeview. But these days, there now seem to be more shows that only appear on satellite (and I presume cable).