um, there is more, if you noticed, On Straxus' slide it said WAVE 2 PREVIEW, and we don't actually know 100% what wave megatron belongs to, THAT IS JUST SPECULATION
how? by preview it means it is just a taste of what is to come, we can not be for sure what is in wave 2, hell, megatron might be wave 3, that could be why we didn't see him at toyfair it all boils down to is speculation, we don't turely know what is each wave, except wave 1, which is at least thrust and drift (prime and bumblebee fit in one of the waves, i think at least prime was wave 1)
Or it could mean, since they didnt have hard copies of Darkmount available, that it was a preview of what the wave would contain