Shug, earlier in the thread you said that the English Premiership is a three team league. It is true that Man U, Arsenal and Liverpool have been the most consistently successful clubs in English league football in the last ten seasons. However, if you compare the number of teams that have finished in the top 4 of the English Premiership in those seasons with the number of teams that have finished in the top 2 of the Scottish Premier League (which I think is a fair comparison given that it is roughly half the size of the English Premiership) you will find that the English Premiership is a more competitive league than the Scottish Premier League.
In the last ten seasons 10 clubs have finished in the top 4 of the English Premiership: Man U (winners 7 times, runners-up twice, third once), Arsenal (winners twice, runners-up 3 times, third once, fourth once), Liverpool (runners-up once, third 3 times, fourth 3 times), Newcastle (runners-up twice, third once, fourth once), Blackburn (winners once, runners-up once, fourth once), Leeds (third once, fourth twice), Aston Villa (runners-up once, fourth once), Chelsea (third once, fourth once), Nottm Forest (third once), Norwich (third once). Furthermore, in that decade three of the clubs that have finished in the top 4 have also been relegated (Norwich, Nottm Forest and Blackburn).
In the last ten seasons four clubs have finished in the top two of the Scottish Premier League: Rangers (winners 7 times, runners-up 3 times), Celtic (winners 3 times, runners-up 4 times), Aberdeen (runners-up twice) and Motherwell (runners-up once). Furthermore, the last time a team other than Rangers or Celtic finished in the top two was in the 1994-95 season (when Motherwell were runners-up to Rangers).
There is a danger that the English Premiership may become a three-horse race between Man U, Arsenal and Liverpool but even if Newcastle fall by the wayside like Chelsea and Leeds have done the big three are still beatable. Man U's defeats to lesser teams last season received a lot of coverage but Arsenal lost a few home games and they won the title because their post-Christmas form was as awesome as Leeds United's form was awful. The Scottish Premier League has become a two-horse race and it isn't even a good two-horse race because one of the runners usually wins by a good distance. To change the metaphor, Celtic and Rangers are the biggest fish in a very small pond but England is a much bigger pond and its top teams are bigger fish and that is why they regularly reach the later rounds of the European club competitions whilst Celtic and Rangers get knocked out.