75 characters is a weird condition. the main thing of a campaign is to show the signature with links as many as possible. The kind of post doesn't matter.
It's not. The main thing is to cut down on people making low quality next to zero effort posts. Should they pay or encourage people to post just smilies or one word replies? No. This restriction is a way to try combat that and at least make people pout some effort in past a few word posts. People can still make those posts but they just wont be paid for them.