But they do come more succesful. Take another look at those trophy cabinets.
They may resemble the backdrop for a production of Aladdin, but amid the rows of silverware both Old Trafford and Barcelona's Nou Camp can boast only one copy of the European Champions' Cup.
It is not much, not compared with Real Madrid's six or Milan's five. Even Nottingham Forest, a club with relatively meagre resources, have won the continent's premier club competition twice.
It is time, then, for United and Barcelona to live up to their reputations and this year offers a genuine opportunity to do so. Milan, the dominant European force of recent years, may be on the wane and tonight's protagonists at Old Trafford are among a clutch of clubs - including Ajax, Paris St-Germain and Bayern Munich - who could benefit.
First, however, they must qualify from Group A of the Champions' League. For both, victory tonight would be a large step. United, who lead the group, would then need three points from three games to qualify. Barcelona, currently impregnable at the Nou Camp, would have only to win their two remaining home games.
United have never lost a home tie in 38 years of European competition.
Barcelona have not beaten a British side in Britain in 15 matches since 1960.
Thus circumstances, and the natural attacking approach of both sides, suggest tonight's match could be a classic. A capacity live audience, and an estimated 80 million television viewers, wait in hope.
Alex Ferguson, the United manager, yesterday said he was anticipating 'a terrific, open game which could go either way. Though I would not want to build them into monsters, they have players like Romario and (Hristo) Stoichkov who have proved themselves at the World Cup - the very highest level.'
After a slow start to the season, Johan Cruyff's team are returning to form.
They gained their first away win at Valencia on Saturday to move within two points of the Spanish League leaders.
Their defence, which has rarely looked secure, is weakened by the absence of the injured Albert Ferrer. The goalkeeper, Carlos Busquets, who has been heavily criticised in Spain (not least for his habit of playing in tracksuit bottoms), is the only non-international and appears the weak link in the side.
United may play an all-English defence, with Denis Irwin omitted to allow for the inclusion of more 'foreign' forwards. Under Uefa rules, clubs in European ties are allowed a maximum of five foreign players, at least two of whom must have become 'assimilated' by playing at youth level in that club's country.
One of those assimilated players, Ryan Giggs, is Ferguson's main worry. The Welshman has ankle and knee problems. Roy Keane, who will have a groin operation immediately afterwards if United win, will play. Lee Sharpe, Paul Parker (who is booked in for surgery tomorrow on an ankle injury) and David May are also fit to play after injuries.
United's goalkeeper Peter Schmeichel had been earmarked to sit out the home Champions' League matches to allow another foreigner to play. However, in both United's matches to date, against Gothenburg at home and Galatasaray away, the Dane has made such crucial saves that he cannot be left out. His presence is all the more necessary tonight because of the set-piece abilities of Ronald Koeman and Stoichkov.
Koeman was 'marked' by Brian McClair when United defeated Barcelona three years ago in Rotterdam in the final of the European Cup-Winners' Cup, and Keane may fill a similar role tonight.
Koeman and Rotterdam now bring back less happy memories for English football followers. Yesterday the Dutchman apologised to 'the English public' for his foul on David Platt during England's World Cup qualifying defeat there a year ago last week. 'I was just trying to do my best for my country,' he said.
The memory may be an added inspiration for United's English players, but they are unlikely to need it. 'There has been an edge this week,' Ferguson said. 'They are all keyed up.
'Over the years big games like this have brought the best out of United. To be in competition at this level, to pit yourself against the best, is worth all the frustrations, anxiety and apprehension.'
Jordi Cruyff profile, page 38