Show us the posts that were deleted and I'm sure you will be told why they were.
It is highly likely that their posts were in the Indonesian section, ergo it may be hard for us to asses it. From what I can see, no threads of their were trashed either. If a topic is deleted with a reply of yours in it then you do not receive a notification. If your post specifically is deleted, you would receive the PM I previously mentioned.
The same applies when a thread is moved to the trash can (there's a difference between removing a thread and trashing it). People won't be notified in either case.I also think there are deleting happenings that does not make sense.
No, it's actually the opposite. There aren't enough deletions. 
