Most of these MD80 aircraft are getting on in years... the JT8D is a low-bypass turbofan that debuted in the early '60s with the. Its design dates back even further to the early '50s with the J52 engine that powered the A4 and A6. The JT8D-200s flying on the MD80s have likely been in service as long as 25 years.

That said, maintenance crews for DL in ATL and AA in TUL are both top notch and have ALOT to do with these planes and engines flying as long as they do. I'm guessing these are isolated incidents occurring so close together out of pure coincidence, though age is likely a factor as well.