The "old school" type of cast iron hobplate, and also the type of glass ceramic hob directly derived from that design, controls power output, NOT temperature, although the more powerful types have a bimetallic switch to stop them from self-destructive OVERheating (somewhere above 300°C IIRC, this won't keep you from starting a grease fire and is likely not meant to).
Such control is by employing more than one actual heating element inside the plate, and enabling only a select set of heating elements for a given setting, also taking advantage of series circuits to arrive at lower wattages. This is not stepless, usually such stoves will have 3 or 6 steps available (see http://www.herd.josefscholz.de/7Takt/4_und_7_Takt.html for all the electrical details - German language but comprehensive schematics).
So if you are looking for a "non-binary" stove, look for models (often inexpensive) that have fixed steps in their heat settings.
Actual Rheostats will never be used since they would themselves generate SIGNIFICANT waste heat when operating; the best thing to use for stepless power output control would be a TRIAC circuit similar to a light dimmer - such might be infrequently found because it is difficult/expensive to build (for a power handling approaching 2 kilowatts compared to a few ten to hundred watts in lighting!) at that power level without creating a lot of radio interference and power quality issues (light dimmers are notorious for that already).
The disadvantage of the old cast iron type is that it is very slow to react to control inputs, the advantage is that thin walled cookware can be used (allowing for very QUICK temperature control by taking it on and off the hob, or even using another, cold hobplate as a heat sink!) since the hobplate itself is a big thermal buffer and power output is indeed constant.