But orientation changes? Is that not a general "mobile issue" for you? Or is (are) the WebKit build(s) in iOS doing something specifically bad compared to (say) Android?
Not "right now". As long as you intend to support "retina displays", it will always be an Apple-specific thing.
If you want to support something as general as high-DPI devices, you know, something concrete and not an Apple marketing-term, there are certainly lots of those being made and sold as we speak. They run Android and are not made by Apple.
You might want to consider supporting those as well.
But I'm guessing that Android phones with high-dpi screens that support that query are still at the single digit percentage of browser statistics.
Still: targetting "retine display devices" is wrong for a multitude of reasons. You don't want your website to be tailored for a device which has 4x the number of pixels of another very specific device made by one vendor only. That is not the problem you are trying to solve.
The problem you are trying to solve is creating a DPI-independent site layout which exploits the resolution and estate available, while degrading gracefully on lower class devices.
If your solution to that problem is making your website hardcoded to fit two devices made by one vendor, as long as they remain true to leaving everything pixel perfect as they are now, for all eternity, needless to say, it's not a good nor elegant solution.
It's the "This website was made for MSIE" of olden days all over again, only this time for Apple-devices. And thats just not going to cut it.
(Possibly interesting idea: add some analytics so that you can detect portrait/landscape orientation changes, and report on bounce rates immediately afterwards…)
However, for most of our users, a zoomed single-column layout is going to be less useful than switching to two columns when in landscape mode on an iPad.
On an iPhone, you should see a single-column layout in either orientation using the design we're currently testing.
For example, all mobile web browsers should theoretically throw either a resize or orientationchange event on orientation change, but some Android devices don't, with no other viable fallback, and no clear rhyme or reason as to which devices support it and which don't (other than that newer flagship devices are slightly more likely to be standards-compliant). CSS media queries are more consistently supported, but they aren't the solution to every problem.