Couldn't comment on the blog itself, but Gmail simply uses Google Closure and its compiler to get minified Javascript + DOM.
And it so happens that Closure code tends to create a ton of extra DOM structure within the JS code, so the 50-level-deep <div> tree isn't much of a surprise, especially with something as complex as the Gmail UI.
In the web inspector console on any open gmail page:
> gmonkey.info("2.0")
"The "gmonkey" module is not officially supported and is subject
to change, we will support previous versions for at least 1-month.
Use gmonkey.load(v, callback) to load in the full API where v is
the version number of the API you want passed to calback. Latest
set of the bindings is "2.0". kthxbye"
GmailGreasemonkey is definitely useful to any Gmail extension developer. Unfortunately there really isn't much discussion happening around updates and you end up running into little problems such as ready().
Well.... I'm pretty sure Google doesn't want you doing that, so it's no surprise they didn't make it easy (and perhaps even went out of their way to make it hard)
And it so happens that Closure code tends to create a ton of extra DOM structure within the JS code, so the 50-level-deep <div> tree isn't much of a surprise, especially with something as complex as the Gmail UI.