Ah the old history started in 1992 point of view story.
The respect for Liverpool comes from what they achieved prior to 1992. Why would United fans restrict themselves to the Premier league years?
United's rise to the top really started post World War 2. We will never forget Sir Matt, the Busby Babes, Charlton, Law, Best.
United's supposed failures between 1969 and 1989 did include 3 FA Cups and we were always near the top of the league.
Compare that to City's 35 year drought. Not just no trophies, they even failed to get to the final of any major trophies for 30 years.
Looking at United's trophy famine 1910/11 - 1947/48 (37 years) and City's 1975/76 - 2010/11 (35 years) here's some points.
1) United's includes 11 seasons lost to the World Wars, meaning 26 seasons cupless. You can't blame United for not winning cups if none were played.
2) Each season United could only win 2 major trophies (League, FA Cup) while City could have won 4 (League, FA Cup, League Cup, Europe).
City's drought was more than twice as bad as United.
Yes both clubs have a history, but history can be success or failure.