Some Petcos only offer the $1 per gallon on common tank sizes. Breeders, longs, & bookshelves, are not a part of the sale. I believe 10g, 20H, 29g, and 55g were the only ones they offered at the location nearest me.
Concerning the timing of the sale, they've held it at least once since the one in July of last year, at my location anyway. If you search the forum history, you should be able to track when the sales are typically held, as someone here always starts a thread letting everyone know when they happen.
As far as that article regarding the $1 per gallon sale being a ripoff is concerned, it's comparing new vs. used, and is therefore a pointless argument. Like someone else said, apples & oranges. It's a great deal for new glass, but obviously nothing compares to (fair) used prices (though many people seem to think they can get near retail for their used tank setups). Also keep in mind that used tanks are much more likely to leak, more likely to have chemicals, disease, snails, etc in the tank/gravel/decor that may show itself once the tank is filled, more likely to come bundled with parts, gravel, decor, etc that you aren't going to use and will end up replacing anyway, basically, the potential for more hassle than new equipment. While I admit, I almost always buy my tanks off CL now, I completely understand why people would rather purchase their equipment brand new, and with that in mind, $1 per gallon for the glass is far from a ripoff.
Personally, I have a bunch of spare equipment from tanks I no longer have, other deals I've gotten on CL, free stuff from people getting out of the hobby. I've got a spare Fluval 404, a Rena XP2, multiple Penguin Bio-Wheel 350s & other HOBs, a handful of heaters ranging from 50-300w, and extra PC & T5 lighting, all just sitting in the garage collecting dust. So a brand new tank, fully set up with quality spare gear, only costs me $1 per gallon. To me, that's a pretty good deal!