Alex, someone familiar with the system you are using could be a lot more helpful than I can. The regulation of flow is done in a couple different ways, with some just being a needle valve against a seat, and the gas escaping through a small orifice after the needle valve. It is the diameter of that orifice that limits the upper end of the flow. When the needle valve is barely open (burner is on lowest simmer), the orifice is not the limiter for flow. When the needle valve is fully open, then the orifice becomes limiting.
[The orifice diameter is designed to match the flow of gas with the air ducted into the burner to get clean burning. But, if the air ducted in is excessive, then the temperature of the flame will be lower because the combustion process has to heat up "extra" air, beyond what is needed to combust the fuel. In addition, because the orifice for a butane stove will be smaller than the one for a propane stove, if you use a propane fuel source on a butane stove, you will get less fuel flow than optimal, and hence lower total heat output. In short, these two effects combine for a lesser heat output.]
Other systems use a step-down pressure regulator (sometimes very primitive) which reduces the pressure at the needle valve control, partly for safety reasons, and (I think) partly to provide for better control of the flame. The larger propane bottles (8 lb and up) use these, and have a flow prevention device in them, also, which reduces the likelihood of a massive leak. I use large propane (actually LPG) cylinders a lot on our household BBQ, and these flow prevention devices sometimes stick closed, and need some "persuasion" to work.
I think the small propane cylinders you are using do not have any flow prevention device or pressure regulator, and just rely on a needle valve.
Wiki to Propane: http://en.wikipedia.org/wiki/Propane
Link to language below: http://www.cpsc.gov/cpscpub/prerel/prhtml02/02127.html
"An additional industry standard (adopted in 1995 at the urging of CPSC) provided for several safety features in the gas grills, hoses, and connections. The safety standard calls for a device to limit the flow of gas if the hose ruptures; a mechanism to shut-off the grill if it overheats; and a device to prevent the flow of gas if the connection between tank and grill is not leak-proof. People who have grills that do not meet the 1995 standard should either get a new grill or be especially attentive to the safety tips below."