"Real business"es have to have the probability of being obsoleted by new startups, or else you end up with a cash factory that spits out investors that cover half the world: http://imgur.com/Bg1SV3g
They have a chance to become a dead pool in this simulation model, more or less approximating that. EDIT: I was wrong, see below.
Currently the rule set says only "startup" and "rocketship" can turn into dead pool, not "real business". Adding the "dead pool" rule to "real business" would indeed approximate that. (Or make it conditional to > a certain number of neighboring "startup"s if you like)