Well, if you search around this forum for those supposed bacterial suppliments, you'll see about 1 in 10 people that actually claim they've had results.
I'll explain my reasoning... again.
There are 2 main types of bacteria in a tank that is cycled. Nitrosomonas and Nitrobacter. Nitrosomonas is the bacteria that eliminates ammonia and, as a by-product, creates nitrite. This is the first bacteria that you'll have when you cycle a tank. Once you start getting nitrite in the aquarium, that's where nitrobacter comes in to play. Basically, it just converts the nitrite to nitrate, rendering it safe for fish. Now, here's where my reasoning comes in to play. Both of these bacteria require 'food' to live. The nitrosomonas requires ammonia, the nitrobacter requires nitrite. If they don't have their 'food', they will soon die. Now, another wrench in the gear. They are also aerobic bacteria. This means they have to have oxygen to live.
So... In a sealed bottle, with no source of ammonia or nitrite... or oxygen, how are they supposed to live? Sure, there may be tons of bacteria in the bottle when it's initially packaged, but what about when you get it home?