I read somewhere that polyurethaned oak floors should be coated with
something every few year, but now can't find where it said that.

Is it true? If so, with what?

The article also said that the recommended material would not adhear if any
wax or polish had been on the floor; my wife swears she has used nothing but
cleaner.

They should be recoated every few years if needed, with Poly or a
Newer non yellowing water base. As in a high wear area as kitchen
halls etc. It depends on how many coats you have originaly and recoating
before wearing through the finish to wood . If you wear through and
catch it quick you may not have to sand to bare wood, that is why you
recoat. I had originaly 5 coats poly, 4 yrs later had it rescrened and
2 more. But Oil base Poly yellows as my floors are much darker. Water
base doesnt. Most finishers put on the minimum as customers dont know
more is better, and many floors wear through in 5 yrs. If wax was used
wax remover must be used and even then there is risk. I imagine many new
sealing and cleaner finishes contain products that may affect bonding of
recoats.
Hire a pro, have him check the floor and products used, and rescreen
and recoat floor several coats. Also gloss is a clear finish, Satin is
not as transparent and a softer hardness, The chemicals used to make
Satin Cloud the finish and make it soft, as in it wears faster.