There is a fair bit of Dreamwave missing, none of FunPub/3H included, and some of the IDW crossovers were left out, but I think they got all of the Marvel US and UK (when they expanded to 100 volumes)... so yes, IDW have produced over half of the licensed comics that were sold in stores, and I remember a few years ago there was a big announcement that IDW had officially produced more material (or issues?) than any of the previous license-holders.

At the bottom of the TFwiki page for this series they break it up the different volumes into their eras and publishers... so you can see the different amounts, that are released so far in the UK.