That line has always struck me funny. The idea of being slowly, painfully digested over 1000 years sounds absolutely horrible... until you realize that you're not going to live nearly that long anyway. It's one of those things that just doesn't withstand scrutiny.
Maybe the Sarlacc's digestive fluids include enzymes that somehow keep the victim alive indefinitely, so it doesn't spoil while it's being digested. That, I suppose, was the idea (or again, more likely, they just didn't think it through). That would be pretty sci-fi, though. A state of suspended animation, but you're conscious and being digested the whole time. Pretty sick. Kinda like how spiders paralyze and wrap their prey, which is technically still alive until they start ingesting it.
Anyway, I tried to get all of that across in a quick, smartass reply, and obviously it didn't work.