I'm not saying everything is art, I'm saying it all can be. And "art" as a noun suffers from a terrible burden of having to share its letters with an adjective which means, basically, "a made thing which I think is pretty" (we exclude the natural world from art -- art is always something a human being does).
I mean, seriously, let's consider this.
This is art. So is
this,
this,
this,
this,
this,
this,
this,
this,
this,
this and
this. Some of this is world-changing, some of it is totally frivolous, some is good, some is bad. So what? What would we gain by saying any of it isn't? What, for that matter, do we gain by saying that it is? Why does it matter that any of these things are art? Why does it matter that things which are similar are not art?
To look at rob's terms, I think they cover two sides of the simple art coin. "Artistic" is, in my experienced, used to describe something done in a particularly pleasing way, "artful" used to describe something done with noticeable skill. That these terms are often used to describe an aspect of something which the speaker does not identify as art serves only to highlight that there is art to be recognised in all human endeavour.
Sokal is right in that saying "everything can be art" is doesn't resolve any real questions about individual objects, but then neither does holding every object up to the light and labelling it "ART" or "NOT-ART". It's a nebulous concept that is used to convey a set of value-judgements that are inherently entirely subjective. It's self evident that what appeals to one person's artistic sense will differ from another's, and that simply because of this we cannot define it meaningfully aside from the subjective experience of the individual.
Where we can meaningfully make the rubber hit the tarmac is in the appreciation of individual works, be our verdict on them that they are sublime and beautiful or a load of old tosh. It's in the details that works of art achieve their effects, not in the general inclusion into a category so broad nobody can reasonably dictate where it ends.