Yes - generally they have single and double size baskets and coffee shops will have several portafilters with different basket sizes and spout combinations.
The 2 spouts are usually poured into 2 different cups for 2 individual serves ~ saves them a lot of time if the shop is busy
I usually request the double basket though as I like it strong and as far as I know the price is the same regardless of basket size. Not everybody likes it strong though.... remember too, the flavour/strength depends on the bean quality, freshness, storage, blending, roasting, coffee machine but most importantly, grinder and barrista skill ~ it all gets a bit complicated but there's a whole underworld of individuals who take it as seriously as charting and analysis!!!
I know a few guys who love this sort of stuff and roast their own green beans in old popcorn makers
I'm not a trained barista BUT I roast and grind my own coffee and have a pretty good knowledge of the process.
All coffee is based around the espresso (shot) which has some very precise technical specifications. Here is a definition ...
A double shot of Espresso requires 1/2 ounce (14grams) of finely ground coffee to be tamped into a filter holder. Then hot water, between 88C and 92C is forced through the tamped coffee under at least 9bar of pressure (at least 130PSI). It must take between 20 to 30 seconds to extract one fluid ounce (30ml). A single shot is 7grams, tamped, same water temp and pressure but usually a shorter time.
The norm for baristas is to pour double shots, as this gives consistent results (something that is harder to achieve than you would think).
To answer your question you aren't being cheated with the double spout pouring two shots and the barista should be using no more or less coffee with this portafilter (filter holder). However, single shot portafilters do exist and then 7g of coffee should be used. When you order a large coffee size multiple shots will be required.
As you can see I'm just a little passionate about coffee.
Yup, definately a lot more to coffee than just appreciating it. One of my mates spent about $2K on a new Mazzer grinder late last year... had his tamper made and measured for the basket, whizz bang top end Bezerra machine, etc, etc... don't think he roast his own though as there is a Merlo factory that roast fresh just around the corner from our office.
Not cheap if you want the top end stuff, but certainly worth it if you can afford it and are prepared to take the time to learn how to use it properly.