Pluggable parsers, automatically good error handling and spidering functionality (finding and queueing new links to scrape), great logging, progress stats, exports, pause/resume functionality, and a million other goodies that are seemingly "trivial" but really you don't want to rewrite them every time you write a scraper.

edit: Especially if your scraping jobs take a LONG time - days and weeks, this stuff is extra handy. Might I add a great debugging environment (scrapy shell), error handling, rate limiting, respecting robots.txt, so much more.