Text Understanding from Scratch [pdf]

> Many times it is hard to find the PDF for the paper if you only have the abstract for a paper.

I agree in general, but it is not so on the arXiv, where one of the most prominent links on the abstract page is "Download: PDF" (assuming that PDF is available). By contrast, if you have the PDF, there is no way automatically to get to the abstract (although a minor bit of URL-fiddling does do the job).

For arxiv papers the PDF is available right there on the abstract page. The main reason to link to the abstract page is in case a new version of the paper comes out. Also people tend to avoid PDF links.