Grammatical neutrality

I'm off on another grammar whinge (actually, only the second on this blog, but unlikely to be the last).

My favourite offender, Pet Supermarket, warns me about the perils of Christmas in the following terms:

Your cat is likely to hide if there are lots of people or noise around the house at Christmas. Give them time and encouragement and they will hopefully venture out and be included so they too can enjoy the Christmas festivities ... If your cat is nervous and hides away, make sure they either have access to the outside to toilet or the use of a clean litter tray.

Now who are "they" - all my clamourous but timid guests, queing nervously in the shadows outside the bathroom door? No, "they" are my cat - he, she or it. I know we aren't allowed to say "he" any more when we mean a person of unspecified sex (just try doing it when you write material for a training course or a company's business management system). But now, it seems, we aren't even allowed to refer to an animal of unspecifed sex as "it". We are, however, allowed risible constructions like those quoted, because it's quite alright to be grammatically incorrect.