This right here ... a 1000 times. I've been a developer for years now and I always held onto the same fantasy of launching something so good that marketing would take care of itself. After building a couple of products and being involved in a startup or two I've found that getting software built is not usually as hard as marketing it successfully
Software Development = Easy
Marketing that Software = Wicked Hard
This is only true because most people are building fairly trivial software.
So I would say, it's only true because Hacker News consists mostly of people who already know how to build software, but far fewer of us know how to market.
For example, in a child comment you mention go build photoshop and get back on how "easy" it is. Problem is more complicated the software, harder the marketing part. In-fact, you might need a full fledged marketing and sales team if you were to successfully launch a complicated software.
But that doesn't mean we should make blanket statements that building software is easy. Because it's only easy if the problem you're trying to solve is easy.
People are paying in proportion to the pain/joy you solve, not in proportion to how hard it is to solve that. The difficulty affects only supply - i.e., if you do make it, how large the competition will be.
Have also written tons of other stuff that this did NOT happen to :)
With software, you can find a way to get it to work. Given the right knowledge, you can accomplish your goal. (Assuming a goal that other people of similar skill have achieved it, and not proving P=NP type stuff.)
With marketing, even if you do everything "right", there's still a huge chance at failure. Being experienced, knowledgeable, and focused doesn't mean you'll accomplish what you set out to do.
I think it's related to the fact that you control software when you write code. Marketing has so much outside of your control that even doing everything right still only results in a < 100% success rate.