That ~ mark means you are seeing the remaining posts of a Member who was either banned or requested their account be closed (I believe some of them
are that). Anyway... It just means you can't star them because that isn't an active account and is officially closed.
Threads stay, as I understand by seeing staff explain this elsewhere, because the Database and nature of the forum system would be compromised if they
started making huge holes all over it by erasing records mid-thread? That's how I understand the second part anyway.
Can't star your posts either. lol. Also looking at your Avatar picture reminded me that I just got through watching a new Dr. Who episode. Woo Hoo.
lol.