I would hope that's not the case but maybe it is. My issue or complaint with that is, once it falls off the list of the (10) shown in the drop-down, I really won't see that thread get updated unless I browse into the (sub-)forum it's in. I never click the "See all..." (alerts) link myself.I believe this is because you've received an alert for this "Appliance" thread previously, but you didn't actually click into that alert and visited that thread. If so, then you're not going to get any more alerts on that thread until you do. At least that is how it works for me.
The alerts do say "There may be add'l posts after this...." too. Almost like the developers added that wording for this very issue ! I guess the alert system doesn't have a way to remove/delete a previous alert ? As in, it alerts me that (#1) "Someone replied to thread X. There may be more posts after this. 1:30pm" and then an hour later, (#2) "Someone replied to thread X. There may be.... 2:45pm" and it quietly vanishes alert # 1 since # 2 now supersedes it.