Nice apples-to-oragnes comparison of the WebM PATENTS to the React PATENTS. The only things they have in common is the scope of the grant. The revocation clauses range from fair and sane in the WebM case to extremely overreaching and unpredictable in the React case.
The WebM PATENTS causes revocation for litigation against Google for patents covered under the grant.
The React PATENTS causes revocation for litigation against Facebook for ANY patent, regardless of whether the patent was covered by the grant or not.
The WebM PATENTS causes revocation if "you or your agent or exclusive licensee institute" sue Google. That's pretty much limited to you / your company / a subsidiary of your company using the code.
The React PATENTS causes revocation if "you (or any of your subsidiaries, corporate affiliates or agents) initiate directly or indirectly, or take a direct financial interest in, any Patent Assertion" - this is where the React PATENTS clause shows it's teeth. "Corporate Affiliate" has a wide definition. For example, a shareholder is a "Corporate Affiliate". So if you own Company A as your startup and use React and also own shares in Big Company B as an investment, then if Big Company B sues Facebook, guess what, Company A loses the patent grant. Or more likely, loses the license and is then hit up for license fees or is then sued if they continue using React.