After reading the story behind the "sharp decline in UK sales" article i decided to check SWTOR MMO performance against the WoWs release.
Its interesting to see that even with the decline in sales and rank in the UK top 40 it still out performed World of Warcrafts initial launch.
In the 1st 5 weeks of sales SWTOR is still in the top 40 (even climbing a bit last week).
Week ending 24 Dec 2011 it ranks 10th
week ending 31 Dec 2011 it ranks 38th
week ending 07 Jan 2012 it ranks 39th
week ending 14 Jan 2012 it ranks 34th
week ending 21 Jan 2012 it ranks 37th

WoW dropped from the top 40 after its 4th week.
It first appeared in the week ending 12 Feb 2005 in the 2nd spot behind (ironicly) Star Wars The Old Republic 2 (which will maintain this lead)
week ending 19 Feb 2005 it ranked 6th
week ending 26 Feb 2005 it ranked 10th
week ending 05 Mar 2005 it ranked 20th
week ending 12 Mar 2005 it no longer ranks
week ending 19 Mar 2005 it no longer ranks