Of course, the Moldau for orchestra has other "colours" of sound than the piano-version. (I have performed Die Moldau in Dezember 2010 with my school-orchestra.)
But the piano-version for me is not minor. Of course, such four hands versions have their sense in studying the great orchestral works, but they also are piano pieces of full worth, with their own artistic and sound-colour refered quality. If a four hands arrangement of a famous orchestral work is "only" used for studies it very often isn´t played too well, mostly played just by site with many mistakes and slips. For me the arrangement of Smetana is worth to be played decently and with the full respect like for a normal piano original work. Further it´s a possibility to experience that great orchestral work alive and may be in a more direct way than as a conductor.
And what does it mind, if Smetana perhaps has tried to earn a small honest penny with it, at least he had to live from something like we all have, isn´t it?!
But here again I was saying this was a wonderful way to study a piece (and consequently, to experience it) in the past.
As for earning the honest penny, why not? Is Stravinsky the lesser because he banked on the Firebird or should we be grateful? I am for the latter.
What Andrew says is true and hence my reference to Chopin.
I feel that I said nothing negative but that does not seem to be the message I conveyed. I am sorry.