I don't think it's matter of 'necessary', I think it's a matter of what's efficient and what's commercially viable. There are probably living bacteria to be found in most if not all of the non-refrigerated products, but in such small numbers that it takes quite a bit longer to establish colonization. And the longer they go unused (sitting on a shelf), the greater the discrepancy. My own experience is that the efficacy of all of the products I've tried is quite exaggerated. And no, I've never used Turbo Start. I might do so in the future, if I can find it when I need it. I'm not going to buy some just to have it sit unused in my own fridge, losing potency every day.
It also depends on the strain of bacteria in the bottle. Nitrosomonas and Nitrobacter species of bacteria are true nitrifiers. while others use Heterotrophic bacteria which are not nitrifying bacteria and will provide little to no benefit establishing a cycled filter.