Yes, pretty common. They are intended to avoid a situation where you post your own copyrighted [1] content to their site, then sue them for displaying it without a license.

The long list makes it seem very broad, but this phrase constrains it quite a bit: "solely for the purposes of including your User Content in the Site." This would prevent them from using your content in an ad, or selling your content to some other company, for instance.

[1] Under U.S. federal law, all content is copyrighted upon creation. I hold the copyright on this comment, and I have granted Ycombinator a license to display it on the HN site.

EDIT - here is the relevant sentence from the HN terms of use agreement. It's actually broader than the language you quoted.

> By uploading any User Content you hereby grant and will grant Y Combinator and its affiliated companies a nonexclusive, worldwide, royalty free, fully paid up, transferable, sublicensable, perpetual, irrevocable license to copy, display, upload, perform, distribute, store, modify and otherwise use your User Content for any Y Combinator-related purpose in any form, medium or technology now known or later developed.