Upward size limit for espresso makers In my, somewhat limited, experience with espresso machines they generally only produce a few shots of espresso per load. 

Is this a technical limitation of espresso making or is it just that the manufactures expect normal, healthy, people to only drink a shot or two at a time?

To put it another way:

Are there machines out there that are capable of producing a pot of espresso or does the process require small batches?
The key here is extraction from the espresso coffee. Only so much desirable flavor and body can be pulled from a puck of coffee. So, then you might say, why not make the puck bigger? Well then that would force the water through a thicker puck, causing the extraction to be slower and longer, giving bitter flavors. The amount of pressure needed to make a desirable "pot of espresso" with a larger "puck" (or probably more accurately, a "slab" in this case) would be a wild safety hazard, since the pressure would be too immense for any cost-effective equipment to handle. 

So, is it a technical limitation? Yes and no. I think it has more to do with being a tried process that gives repeatable, scientific results.