HFT firms mainly hiring mainly PhDs?

Hi, I'm physics postdoc interviewing at the moment with a (reputed) hedge fund / market maker, and I am realising now (mainly checking LinkedIn) that some companies are mainly hiring PhDs in their quantitative research teams (eg. SIG/DRW/DEShaw/TwoSigma/etc..) while some other firms have a majority (or at least a lot) of non-PhDs in their quant teams (eg. Optiver/HRT/JaneStreet/Virtu/TowerResearch/CFM).

Is there any reason for this? From an outsider point of view, the percentage of PhDs does not seem to correlate that much, if at all, with the success of an HFT firm. But the culture may be very different? Since the firm I am talking to is mainly hiring non-PhDs, that is worrying me slightly... Any thought or advice?
Well, it is different, otherwise why would different firms have different hiring strategies. While I absolutely do agree that quants with PhD are not more qualified /better to get the job done in HFT, and are indeed sometimes too theoretical / not practical enough / etc.. I am still interested in the reasons behind these hiring strategies, and if there are typical culture differences among these firms.
Some of the companies think that having a Ph.D. is more than having, say, an MFE. I'm not saying they are right in their judgement. Maybe they think having a Ph.D. shows commitment and intellectual stamina -- who knows? But in a buyer's market -- one in which they are flooded with Ph.D. and MFE resumes -- they get to decide on who they hire. I know that companies like DE Shaw are looking for more than just a Ph.D. -- they want to see some evidence of real ability (such as having done well in mathematical olympiads, for instance).