I think that may explain part of it, but I haven't seen citations supporting it with hard data. I wonder if it has to with chemokine(sp?) coreceptors ccr5 or cxcr4.
I entered (ccr5 or cxcr4) and bubonic plague into PubMed's query box. That was one of 16 hits involving CCR5.
If HIV is completely harmless/does not cause AIDS, you might as well be talking about how many angels can dance on the head of a pin.