I'll answer as founder and developer of Smartsteem.com - biggest vote-selling market with over 3500 sellers and 2nd biggest bid-bot with over 1.4 Million Steempower:

First of all: the post-age limit of 3.5 days was a great change. The only reason some people are against it, is simply out of the fact that they don't like to be told what to do - even if it's for the better.

You want to promote your post for visibility? 3.5 days is more than enough. Afterwards you'd primarily do it for monetary gain

Now - the reason why flagging the users of services and bid-bots which allow posts older than 3.5 days is the only viable way - is because users are less attracted of using those services.

Upvoting users who are doing the right thing by using services which only allow post-age of 3.5 days or less is completely useless as

1.) the amount of users is way higher - which makes the possibility of change a lot more difficult and 2.) the wrongdoers have no reason to change their behaviour and 3.) new users have no reason to avoid these services.

Which altogether would result in not achieving the desired effect of vote-services only accepting posts max. 3.5 days old.

But .. but flagging minnows is wrong?!

Yes. But what good is the word of a man if he goes back on it?

@grumpycat told everyone that he'd downvote anyone who uses services & bid-bots that accept bids & requests for posts that are older than 3.5 days.

Nothing more and nothing less.

And regarding the self-voting: it's his stake and downvoting isn't giving any rewards.