With scrape.ly I can just do this to crawl the entire HackerNews site across pages and grab the urls and extract any data from the page it lands on without defining any fields (it discovers them on it's own) and so doesn't require you to 'relabel' fields when the site changes layouts. It also generates new IP addresses on the fly so you don't get stuck and launches multiple threads for you to speed up the process. It works fully with ajax sites and single page apps. Flash support is coming too.
http://scrape.ly/s/{https://news.ycombinator.com/}
{next:More}{Space Monkey dumps Python for Go}*{fields:'Auto'}
Honest question (I don't mind downvoting if you disagree), but why would you want to waste time writing web scrapers, maintaining it to run and fixing the code? Multiply it by 100 or 1000 different websites and it becomes a full-time job. For me, I want to get the data I need with the least possible of overhead and as soon as possible and I don't really want to be bothered with setting up environments and hosting for it to run and fixing bugs when sites change layout.