It's very likely the hormone that regulates urine production, especially at night (it allows us to sleep that long and not have overflowing bladders) probably hasn't kicked in for him like it does for most children. My oldest son (8.5) is in the same boat and that's what the doc told me. J doesn't have problems during the day thankfully, but he rarely has a dry night. There is also medication available but we've chosen to not go that route.
My lifesaver has been bedwettingstore.com. They have tons of stuff from alarms to mattress covers to special underpants. The underpants are especially good since they look like real underwear (for the most part) so my son isn't embarrassed to wear them to sleepovers (vs. a disposable pull-up). We tried the alarm but it didn't work for us. I think that's because we'd been given a much used model and it was just on it's last legs. We plan on buying a new one this summer and trying again.
Also, if he had stopped doing it during the day for a while but seems to have started again, I would have his bowels checked. My oldest daughter, a few years ago now, start wetting herself and the bed again after being completely trained after a year. We thought nothing of it, because she was still pooping. We were also thinking that she was doing it because it was spring and she was having too much fun to come inside. Well, it got worse and worse until we could go nowhere without a bag of extra clothing and she'd go through several outfits a day as well as wetting herself at night. I took her to the doc for her physical, happened to mention her peeing so much and after answering a few questions the doc sent me to have my daughter x-rayed. I could not BELIEVE how much she was backed up and I felt horrible that we'd been disciplining her for problem and it was actually completely out of her control. Because she was so backed up, it was putting pressure on her other organs, including her bladder. It actually weekend her bladder so now, even a couple of years later, although she rarely wets herself during the day (she does have diminished capacity though) she still wets herself at night.
Your son may also have a bladder infection. I think a visit to the doc is well warranted to just make sure it's not because of an infection, etc. It will help you make your choices better on how to handle the situation. I understand where you're coming from. Having two children that wet their beds almost every night (my daughter is especially bad at wetting her "pull-up" (not the disposable kind but that's what she calls them), removing it in her sleep and then peeing her bed. Sigh... My husband cares for the kids in the morning before school and he doesn't always check that soiled bedding & pull-ups made it to the washer. My house often smells like pee. >.< Good luck!