Because I think these guys are copying both ideas and execution.
It's one thing to say "I want to make a site where people can rent out their spare rooms, I saw some other site do it", it's quite another to say "look at airbnb.com, copy that". When the exact execution is the same (even down to page layouts) you're not actually contributing anything yourself.
Well, I don't know that "Welcome to the real world" matters. No-one in HN is saying that they should be banned from doing it, or otherwise prevented. Just that we, as a community, don't value the people that do it.
Thom are you serious? of course Facebook solves the problem -- before it was hard to easily connect with others on such a broad spectrum. No, they were not first with social platform, "friending", IM, sharing photos, etc, but they did all this in the right time and place plus all the luck they had as a result they are the biggest social network which is a huge leverage on the market. My parents found tens of friends from military, schools, camps that took place 40 years ago, people that they lost connection with because there were no internet and no tools in place that time. So as much as I don't like Facebook and all the ongoing privacy issues, I would say: yes, they did solve a problem!
So by your definition the germans are solving a real problem then. The problem of localization. In other words, they are saving the world.
See the lines are rather blurry. Ultimately everything can be argued as solving a problem. But that is IMO a very unproductive way of looking at things.
Building the site is not the whole execution. There are other business processes they may be introducing and improving upon.
I like the "art" of building businesses and I'm nos sure I'm OK with what they do They are turning the art into an assembly line - all their ventures have high commonality - from information technology to business processes - and that should make them very efficient.
It's one thing to say "I want to make a site where people can rent out their spare rooms, I saw some other site do it", it's quite another to say "look at airbnb.com, copy that". When the exact execution is the same (even down to page layouts) you're not actually contributing anything yourself.