Polished porcelain tiles wear/lifetime

We've been considering what to use as a floor covering for the
entrance of our house (a hallway which is about 2.5metres wide
with a stairway to the left cutting into part of that space).
The polished porcelain (Chinese or Italian) looks very nice.
I seem to recall the tiler and the tile supplier mentioning that
there is some sealer used to maintain the high gloss on those
tiles.

What is the real story here ? Are these a fad ? Given that a hallway
will have highish human traffic what is the true situation regarding
the lifetime of the gloss on (say cream porcelain tiles of good quality)?
Is there a maintenance aspect. eg. is there a sealant which can be
re-applied say after 5-7yrs ?

I'm guessing that there aren't many houses where these tiles have
been down more than 5yrs since they are really only now becoming
more mainstream for domestic.

--Ian