I think the difficulty the parent poster mentions is really meant to be read as:

"Ability to work with poorly defined goals AND almost no one knows about this subject you are discovering".

So of course you could start a new Web App for a customer and have poorly defined goals (good luck with that!), but the problems you might encounter have solutions already fleshed out by millions of other Web App devs (Stack Overflow). Something tells me undergoing a PhD is not quite the same, as the 'resources' in this context are a few orders of magnitude scarcer, and the subject matter a few orders of magnitude more complex ...

(I am not a PhD, please forgive me if this is wrong)