(unless it's burrow micro without detection, which is not realistic)
-Hydralisks are mentioned as a counter to marauders. That is also not true, assuming the marauders have medivacs and stimpak.
-Hellions are mentioned to suck against speed zlings and speed blings. This is also not true
Thors, vikings, and to a lesser extent (especially since 1.1) siege tanks also work vs banelings, since not only can they help kill banes, but they can soak up a lot of baneling hits.