Automattic themselves contribute a hell of a lot of time and effort back to WordPress. There's tonnes of plugins that they've contributed back (http://profiles.wordpress.org/automattic), they often test patches that might break things (with the scale of WP.com meaning they do break, and quickly), and they employ people to work full-time on WordPress. Automattic is pretty much the worst example of a company that doesn't contribute back.
As for the ticket you mention above, that has been deferred because we're still working on the specifics on how to handle that in a backwards compatible manner. This is being handled in a plugin at the moment, with hopes for integration later: http://wordpress.org/plugins/wp-db-driver/
(If there are any specific tickets you want to point to that haven't been accepted, please let me know and I'll re-review them for you. Intense Debate is not an excuse for the built-in commenting sucking, especially since ID is basically dead.)
There is always a "backwards compatible" argument that pops up, but the solution is simple: persons that dont want to upgrade from their 2002 PHP installation can use legacy WP. Everyone that wants a new WP site can just do so using modern server software.
We tried a long-term support branch. It doesn't work with WP's development process, and it's a lot of extra effort. It's not too hard to maintain backwards compatibility on the other hand.
Even automotive manufacturers have to supply parts for cars they manufactured for X number of years after the final production. I hope new 2014 cars don't include parts from the 1940's era for "compatability" reasons.
No 1940s vehicles didn't come with ABS, front and side panel air bags. But linkage in the suspension was at least metal, and wasn't known to fatigue every five years. If I were so inclined I could bring my hick mechanic in here and he would have volumes of corner cuts to cite that have resulted in unnecessary deaths over the years.
Some advancements have been great but overall legacy parts don't engulf vehicles in flames. Hodge-podge workarounds do[1].
SVN repository: http://plugins.svn.wordpress.org/hyperdb/
SVN changelog: http://plugins.trac.wordpress.org/log/hyperdb/
Yes, it's not on Github (which is a shame), but that's a long way away from being closed source.
[0]: http://www.gnu.org/licenses/old-licenses/gpl-2.0-faq.html#Wh...