The OLCC says that enforcing the happy ban was impossible, especially when bars could be advertising their sales on Twitter or their own websites which the OLCC investigators don't have time to check constantly. The agency wound up enforcing the rule sporadically.
But, with typical bureaucratic finesse, the OLCC has kept the rules complicated:
In an effort to help prevent price wars on alcoholic beverages to be consumed on the premises, the rule prohibits advertising both the time period (i.e.: 3-6 p.m.) and a price or discount (i.e. $2 pints or 25% off) in the same advertisement.
Oh well. If you have one of those iPhones, there's always Cocktail Compass.