Also I won't be surprise that reddit will add more bots in the comments.

Without an open API, there's no way to verify exactly how many "meatspace" users there are on reddit. This is a key piece of information to hold that, say, facebook has always held close to their chest.

Advertisers ultimately pay for "impressions", and that number can be ofuscated and inflated (ie counting bots) to entice advertisers and IPO investors to continue to invest.

Turning off the API is turning off active user verification.