I think the clutch thing is to prevent the motor being heavily loaded when starting (There's probably a fair weight in the headstock/geartrain of these, even without a big chunk of work in the chuck - though I'm going off memory as I haven't used anything that size for probably ~20 years!!) - and also to prevent the motor being started and stopped loads of times if your doing lots of cuts. DOL starting tends to heat motors up fairly quickly when doing lots of stops/starts. Probably not needed with a VFD as you can have a smoother ramp up, avoiding the large currents drawn on start up.
Yeah single phase motors don't like repeated starting but I never blew one up yet. I wonder if most of the gubbins isn't for running the hardness of the clutch engagement?