The preview seems to be limited to 30 pages for some reason. However, if you have a longer document, and export a PDF via the export-menu, that PDF will have all the pages.
There is a question about this in the feedback-forum. It is from April 2012, but no replies yet:
As mentioned by Werner in a comment, one of the developers has said that the 30-page limit is somewhat arbitrary:
I'm a cofounder at writeLaTeX.
We don't currently use a background daemon. Our backend uses pdflatex on Linux, so I can't say much about XeLaTeX on Windows (but XeLaTeX support is planned), but here's our experience.
The main factor that determines the compile time for a small document is whether the many source files for the packages it uses are already in the linux disk cache. (See http://www.linuxatemyram.com for an overview of the disk cache and some good links.)
That is, the first latex document you compile tends to be slow, because latex has to read all of those files from their various locations on your hard disk. But, when you compile the second document, the operating system has helpfully kept those files in main memory since it read them the first time, so reading them in again is much faster.
I also know that jpallen of ShareLaTeX now maintains the CLSI, which is open source, so you can see how that backend works. I don't think it uses a background service, either.
As far as I can see, the daemon-based approaches in the links you provided still work in principle, but I don't know whether they're still supported.
2020 Edit: Most of this is moot now, since they merged a while ago. In the end, ShareLaTeX won, and took on the catchier Overleaf name.