Ebert seems to want to decide what art is and isn't by way of taste, but that can't be. if what art "is" can be discerned through subjectivity, then nothing is art. nothing. my understanding of art is this: "a creation who's only purpose is itself and it's audience."
Cars, beautiful works of engineering and aesthetic, something people the world over are passionate about, are not quite art, but a Ferrari 458 Italia's staggering beauty could be construde as a work of art, even though the object itself has a purpose beyond it's audiences enjoyment: it gets you from A to B. there is valid arguement on both sides of the debate as to whether or not a sportscar can be considered a work of art.
this is one of the only reasoned arguements there can be had on where the lines of art blur, because at the end of the day, "art" is not great. it's not pretty or perfect or what you or i say it is.

Deuce Bigelow: Male Gigolo is a piece of art.

Baby by Justin Bieber is a piece of art.

Liesure Suit Larry: Box Office Smash is a piece of art.

these are for all intents and purposes utterly dreadful things. they suck. they're annoying, they are utter failures, but they are art.
i've never understood the instinct critics and artists alike, have for sanctifying the word "art" as something to be bestowed only upon the holiest of holy works. the debate that derives from this way of thinking is childish and arbitrary. it serves no purpose and it's unmoveable. if Art is what you, or i, or Roger Ebert, or anyone decides it is based on cultural and personal signifigance, then art doesn't exist, and all this stupid squabbling is for naught. nothing can be art under this doctrine, because it is vague and overpersonal.

it's time to stop putting art on a pedistal, time to stop using the term like an ordainment or an echelon. art is terrible, art is great, art is creation, even lazy, stupid creation. video games are art, the bad ones and the good ones. now shut the fuck up.

i'll leave you with a quote from a movie Ebert gave 4 out of 4 stars:

In many ways, the work of a critic is easy. We risk very little yet enjoy a position over those who offer up their work and their selves to our judgment. We thrive on negative criticism, which is fun to write and to read. But the bitter truth we critics must face, is that in the grand scheme of things, the average piece of junk is probably more meaningful than our criticism designating it so. But there are times when a critic truly risks something, and that is in the discovery and defense of the new. The world is often unkind to new talent, new creations, the new needs friends.