What is the reasoning behind only an itemid in the URL for HN?
It's easy to code
Is there an SEO impact?
Probably, but as SEO is search engine optimization, if a site doesn't care about search engines, then it also probably doesn't care about optimization of those searches.
It's easy to code
Is there an SEO impact?
Probably, but as SEO is search engine optimization, if a site doesn't care about search engines, then it also probably doesn't care about optimization of those searches.