(A) I'm the only person to use the term "fucking stupid" and it clearly refers to the concept that an episode preview is a spoiler (comparing it to saying the OP/ED is a spoiler in that same way), not an individual. The reasoning, not a person. But hey, egotism. I called you a whiner only...which ya are.
(B) Previews are not always at the end of the credits. They're quite frequently in the middle of the ED, so they're most certainly not commercials that just "happen to air right after." They are part of the episode. I can't believe how many times we have to reiterate this.
edit:
Since you'll just refuse to believe me, some examples:
- Suisei no Gargantia
- Magi Season 1