Nice to have you here on the SEO forum, Cata.
Sorry, but my English is not very good 😀
I think that SEO for Google.nl is nothing else than SEO for Google.com.
You are right. Lot of the backlinks are made by webmasters who do submit a link to a “startpagina” or “directory” as you call it. There is a lot less competition here in the Netherlands, so if a site would be banned by Google or penalized, it won’t have a big impact in search results. Ranking on Google.nl is a lot easier than it is in Google.com, at least, that is my opinon.
Pretty interesting question. I would love to talk a bit more on this in-depth.
Sorry, for the bad English!