The rail system isn't ideal for many cases. Perhaps for mounting dichroics but what about building diode modules, etc. A one size fits all approach won't work for everything. The purpose for the adjustable mount is so once the mirrors is glued, one can still adjust it, so glue certainly is necessary for affixing ones optic. Again if all optics were the same size, then it would be possible to design mounts to fit the optics, but so many different shapes and sizes are in use.
On a side note, has anyone worked with the cheapo goldenstar flex mounts ? At $5 they're hard to pass up on, but have always been to skeptical to use in builds. Anyone have anything good or bad to say about their stability ? How close to a regular flex mod ?