A guard over the top of the wheel wouldn't do much. The left side of the wheel is the side used. This can result in a ricochet effect off the table. Safety glasses are mandatory.
The relative safety of such a power tool rests not in any state-mandated guards but in the actions of the operator. You need not work around fast RPM abrasive machines very long before you learn how dangerous they can be. I use this disc sander to round edges like the table itself and the angle iron base. All those rounded corners were done on this disc sander.
While building this disc sander I was de-rusting the 3/8" plate using an angle grinder fitted with a standard cup wire wheel. I was wearing my regular denum shop apron. Leaning over for all this caused the shop apron to hang a little too far forward and it got caught in the 11,000 rpm wire wheel of the angle grinder. Happened real fast and ripped that apron right off me. It stalled the grinder right now. (notice there's a guard on the angle grinder... for all the good it did)
Bearing life: Harbor Freight bench grinder $50. What would the replacement cost of the bearings be? If it was over $20 it'd be more prudent to just replace the grinder. However, bearings are relatively inexpensive. I'm 60. If I get 5 years of use out of this disc sander it will have been a good cost return. My lathe tool grinder is a Craftsman 1/4 hp I bought when I was 19. The bearings are about shot and it'll be replaced very soon with a bigger hp unit. Forty years out of a $20 Craftsman grinder ain't too shabby considering the hard use it's had.
I appreciate concerns over safety. I worked 23 years in a diesel maintainece garage for Los Angeles County Metro, 10 of those as a leadman. Some accidents result in death in such a place. I was pretty hardcore when it came to looking out for the people on my crew, sometimes to the utter contempt of ~management~. I never lost an argument over safety because I knew the job better than anybody else and I took responsibility every time I said 'no' to a supervisor.
I don't mind someone raising an issue of safety. But you better do it in plain English without hyperbole. You'll find I'm a capable communicator but I won't suffer fools.
This disc sander was built in July, 2009 so it's had almost 2 years of use. It's been an excellent addition to my shop.
Dutch