The "vertical-align" property only functions as a general vertical alignment tool in table-cells. Now that we have "display: table-cell" in basically all modern browsers, this is more or less sufficient, but it's still a far cry from being as simple as you've made it out here.
Columns are HUGELY more complex to build than they have any right to be, and they are fragile in any number of cases where they shouldn't be. Support for true multi-column content panes is far from where it should be.
Saying "the developer builds their own" is the same as saying "one is not provided." Whether it should be provided is a worthy argument, but it's not a foregone conclusion, and calling the OP a poser isn't remotely justified here.
Doing rich interface design is unquestionably clunkier in HTML/CSS/JS than in dedicated GUI toolkits on the desktop; I don't agree with the parent that it's not suitable for any real work, but your dismissing him out of hand isn't remotely fair. And it's pretty clear that he's not a "poser web dev," but rather a native dev who's used to more explicitly specified layout mechanics (that is, not having to work around the assumptions inherent to HTML as a descendant of a width-specified static document format.
Is it? I've never had a false positive in all the years I've been using GMail.
That you noticed. There's a fairly high bias inherent there; it just has to not have hit something that was both noticeable and that you knew was incoming.
But there's a trade-off between less code run and less code written (by you, that needs to be looked at to maintain/debug). You have to make an informed choice about performance vs available time and visible complexity. jQuery et al. arel going to turn out much smaller blocks of code (that have to be written, and later read by the maintainer) for a lot of common operations. This is especially true if your support window includes IE or mobile.
There are a lot of tasks where using a resource (that's likely already in cache, if you're loading from the CDN) to smooth over AJAX handling or deferred event assignment is absolutely more valuable than making it so an operation that runs maximum three times per pageview can run a billionty times per second. And there are times when it would be stupid.
If you think the system is working, ask someone who's waiting for a prompt.