Acrylic doesn't oxidize like vulcanite, but it does break down in time. Think about how clear acrylic stems yellow on those clear GBD pipes, even when they haven't been smoked yet. According to emcoplastics.com, acrylic will start to discolor in 10 years, although on black stems you won't notice. After 10 years it also slowly starts to become more brittle.
Back in college, I worked at the BMA, and would replace the UV acrylic sheets used by the museum here in ten year intervals, because they would start to show signs of slight yellowing. And, the old sheets were very easily broken in the process, whereas the new sheets were more springy and pliable to work with.
Yeh yeh, vulcanite is more maintenance, but in the long run, I think it vastly outlasts acrylic. I'm not sure how long the industry has been using acrylic stems, but it is not nearly as long as it has used vulcanite. It may be a few more decades for the material to deteriorate in stem form enough show visible signs of age.