This may not be a big deal for a toy game like Tetris. In a multiplayer AAA game it could lead to a bunch of bitter consequences though, from malware pwning customers' computers to ruined multiplayer experience because the bug would affect the server.

I'd say that a memory safety bug is not like a blemish on the surface of a building, unsightly but tolerable. It's more like a crack in the foundation, which may look tiny on the surface, but who knows how deep it goes.