Actually, I believe that is the key to it.Also, Cardiff didn't have Will Greenwood baying for him to be cited!
It does seem to me that commentators/media unduly influence the whole disciplinary process.
We certainly saw that in 2002 when - following a media outcry - the RFU overturned their procedures in order to ban Martin Johnson for his punch on Robbie Russell, setting a precedent that entirely changed the way the citing process worked.
And we see it now, where two almost identical incidents are treated completely differently. Both were televised games, so that's not an excuse. But the difference is the reaction of the commentary team.
Tuilagi's incident was replayed with comment about how illegal the hit was. Result? Citing.
Shanklin's was replayed with Jonathan Davies denying the evidence of his own eyes to claim that Shanklin did nothing wrong. Result? No citing.
There is something seriously wrong when the media have such a level of control over the disciplinary process.