MAS only operates MH 7/8 (the third flight) on Tuesdays, Wednesdays, Saturdays and Sundays. On Mondays, Thursdays and Fridays, MAS only operate twice daily to Kuala Lumpur as MH 2 and MH 4. Hence, they are not shoving both ZRH and LHR passengers into one flight.
Plus, if I am not mistaken, MAS have higher loads on the night flights, i.e. MH 1 or MH 7 compared to MH 3 since most Australia bound passengers prefer the night flight. MH 3 are mostly catered for people traveling to Kuala Lumpur or with onwards connection to other Asian cities or SYD/MEL only. If I am not mistaken, it's only in November last year when they merge MH 7 and MH 1 together due to excess capacity in London after the Sept. 11 tragedy. After that, I don't recall them doing so.
LHR and CDG are probably doing pretty well for MAS, so much so that MAS wanted to increase their flights to London to 3 times daily and daily flights for Paris. I think Amsterdam is doing pretty well for MAS as well, thanks to KLM. MAS might have a bit of excess capacity at Frankfurt though. I have no idea how Zurich/Rome/Vienna/Manchester is doing, but as from what I heard, Zurich probably have quite a lot of premium passengers.
Bapilot2b: That's where I gather my information.