I wouldn't say Hatris or Hypernova Blast are sequels. The former is just another falling brick game from the same guy and the latter is more of a slightly upgraded port.
Hatris was the only way for the real creator of Tetris to make a sequel. If Liquid Kids, Phantasy Star II, Son Son II, Super Mario Bros 2 USA, Vasteel 2, etc count as sequels, then Hatris might as well.
I do think that many games are both enough of a sequel and a remake and consider them within the realm of both.
Hyper Nova Blast has the full effect of the thread's subject, in that most Turbo players are unaware of the original game. It's similar to Star Soldier/Super Star Soldier.