First of all, for those not familiar with zRAM, it's a Linux kernel module (formerly called compcache) that tries to better system performance by using a compressed block device in RAM in an effort to avoid swapping/paging on disk. The zRAM kernel feature is intended for systems with low amounts of system memory. With the Linux 3.8 kernel, the zRAM feature will leave the kernel's staging area.
While RAM is rather inexpensive, there's still users and developers wanting zRAM to be used by default within Ubuntu in some manner. Within certain cases -- such as for the Ubuntu Nexus 7 and other certain ARM images -- zRAM is already deployed, but it's not being done so at this time within the stock Ubuntu x86/x86_64 installs. The zRAM kernel configuration option is present and there's the zram-config package within the Ubuntu package archive, but the Ubiquity installer isn't configuring it for use. The zRAM capability is mostly a win for netbooks/mobile devices and other cases with very restricted amounts of RAM.
The Ubuntu zRAM discussion was brought back up yesterday on the ubuntu-devel-discuss list. The discussion is still active, but if zRAM is to be deployed within Ubuntu on a larger scale, it will likely come down to a feature that's determined at install-time. If the system's available RAM is below a certain amount, the zRAM feature could then be enabled with zram-config while keeping it disabled for those with modern computers having several Gigabytes of system memory.
There's also this Launchpad bug report going back to 2009 about enabling zRAM/Compcache by default. We'll see what happens as the discussion continues and whether any change is warranted for Ubuntu 13.04.