Was in an immaculate Lufthansa B744 recently that both looked and smelled new.
Are you sure it was a 747-400? Lufthansa picked up 19 747-8 in the last few years and they don't look all that much different...
As noted previously, Singapore likes to keep a young fleet, and frequently gets rid of aircraft when they come up for 'D' checks.
Are Singapore's A380's leased? if so the lease is probably up and they simply walked away...