Far be it from me to speak for Patrick, but generally the sales pitch for this sort of arrangement does not sound like "Hi, I'm a programmer. I'll build anything you want if you pay me 2% of your company's profits this year." It's more like "Hi, I'm a business consultant. I possess a specific set of skills which involve using software to increase profits for businesses such as yours, often by as much as 5%. My services cost an amount which is comparable to 2% of your current annual profits." (The numbers in that example were picked at random, but obviously the return needs to be higher than the investment for things to work.)
In other words, it's pretty uncommon (and generally ill-advised, IMO) to ask for a "% of profit". What you are doing is anchoring your price tag against the value you can create, instead of the time you spend. (This is somewhat muddled by the fact that consulting engagements are generally billed by multiplying a dollar rate with the amount of time over which the engagement took place, but the only number that matters to the client is the one at the bottom of the invoice. It is the consultant's responsibility to find clients for which that last sentence is true, and to make sure that they are able to consistently generate positive ROIs for those clients most of the time.)
In other words, it's pretty uncommon (and generally ill-advised, IMO) to ask for a "% of profit". What you are doing is anchoring your price tag against the value you can create, instead of the time you spend. (This is somewhat muddled by the fact that consulting engagements are generally billed by multiplying a dollar rate with the amount of time over which the engagement took place, but the only number that matters to the client is the one at the bottom of the invoice. It is the consultant's responsibility to find clients for which that last sentence is true, and to make sure that they are able to consistently generate positive ROIs for those clients most of the time.)