I've always thought City supporters misread the reason for that result.
We were on the brink of qualifying for the Europa League that season via the Fair Play League as long as we did not pick up a few yellows or a red during that last match against Boro. This would have been the first real participation in a European competition for quite some time and would help attract better calibre layers in the summer, especially as we had some purchasing power for once (I'm not counting the farcical appearance in 2003 where we went out to Grodzisk in the second round).
My reading—especially having watched the entire match and noting how sheepish we were in the tackle the entire time—was that the players were instructed, in no uncertain terms, to be "good little lads" and thus gave Boro the run of the land. The fact that Sven and the players knew he was off was relatively inconsequential to the 8-1 outcome. Sven was already gone and the focus was getting European football so it could have been a a cricket score and would not have changed anything. Now, had the players not followed instructions and picked up several bookings there would have been repercussions beyond Sven's sacking, especially if you believe some reports that Shinawatra had been shopping the club around and wanted to use European football as a sweetener.