I can't speak for other Dev's, but I had prostate cancer that spread to the surrounding tissue 3 years ago and underwent extream radiation and hormone therapy that, while eventually proved effective to kill the cancer that wasn't able to be removed during my prostatectomy, also left my immune system devastated. It basically reset my lifetime immunity build up to zero. Add to that the fact that my daytime job is as the head custodian for a private school and I interact daily with hundreds of little walking petri dishes of random illnesses and yeah, I'm sick pretty frequently... However, not being a fulltime dev, my "sick time" mostly effects my day job...
P.S. I had my 3 year 0.001 PSA test result in July and am officially in remission. Even though I still deal with lasting after effects of the cancer, I plan to be around for at least another 20 years.