I was thinking about how other than the Okogwu/Verhaeren murders (possible Moriarty connections) and Poirot's newest case (Sweeney Todd), their cases seem pretty unrelated from the main narrative of the ARG.
Trying to find connections, I further realized that other than the cases which caused the two of them to meet (Okogwu/Verhaeren murders and the masquerade ball at the Plaza) and the Sweeney Todd case, all their cases had to do with altered documents and allocation of finances:
Holmes found that Maureen O'Shea's coworker altered the company's documents to make it look like it was she, not he, who had been embezzling the funds.
Poirot found that Cavaignac's wife destroyed his new will and orchestrated his murder to prevent him leaving all his money to his illegitimate son.
Holmes found that Rupert Bingley took out the clause in his father's will that prevented Jane from controlling his funds, before murdering his father.
I'm not sure if I'm reaching here, but this seems to indicate a trend (or possibly even a hint about something in a different area of the ARG?). We got to experience altered documents a couple of other times, too-- Holmes' mangled invitation is one, as well as the hacking of first Tara Coulson's blog and then the WTF site by the Cabal.
I'm... not sure where I'm going with this. But I think it might be significant (the documents part more than the financial aspect, which is probably more just tied up with motives).