Don't forget a lot of "piano" music we associate with Beethoven and back was written on the harpsichord and organ. The piano didn't exist.
I'll assume you meant "Bach" -- Beethoven certainly played and composed for the piano
(See here http://en.wikipedia.org/wiki/Fortepiano).
As far as the suitability of playing Bach on a piano (or any other instrument)
Nobody probably thought much of someone releasing a recording of something like the WTC played on piano 50 years ago, but in today's artistic climate, it's regarded as being a bit tasteless, as Bach certainly wrote his contrapuntal keyboard works for the keyboards of his day (be they harpsichord, clavier, or organ).