When it comes to published adventures, there is usually a range for the number of players that recommends 4-6. (DCC RPG certainly ranges higher). That is why in my survey 4-6 players plus GM was one of the choices, and it seems to apply for 2/3 of the gaming groups out there. The question then becomes: "How do you modify an adventure to balance for a smaller / larger gaming group?"
For the larger group (or PCs of a higher level than the recommended level spread) the answer is usually to simply increase the number of adversaries. Heck, some adventures even give examples on how to do so. It's not so easy to modify the power level down, or at least, it's not as intuitive in my experience. Which is probably why we rarely see examples of how to power down an adventure.
Why is this important? Fully 25% of the groups (as per my I'm sure "unscientific survey") regularly play with a group of 2 -3 players plus a GM. Assuming folks aren't doubling up on PCs, we're talking fairly lean in numbers adventuring parties. An adventure that is level appropriate for 4-6 PCs is going to be a very tough for 2-3 PCs.
While I don't expect publishers to aim their products at 25% of an already small market, I can't think of any adventures off hand that have easy conversions notes for accommodating a smaller party.
Before someone states the obvious: "Why aren't you just writing your own adventures?" time is often a luxury I don't have, and a well written adventure is a time saver. Having to rewrite one to accommodate a smaller party can be a PITA. I've done it. Just wondering if there is anything out there that takes into account a larger possible spread in the party numbers, especially on the smaller party side of the equation.