I have a 10" table saw... this is probably a stupid question, but can I use an 8" dado blade set in this saw? Is one only supposed to use 10" blades in a 10-inch saw? I read on some contractor's blog that one should only use saw blades that are within the range of blade sizes acceptable for a particular table saw (per that saw's documentation)... but for the life of me I wasn't able to find mention of the range of allowable blade sizes for this saw last night in reading the manual.
There is NO problem with using an 8 inch dado blade on a 10 inch saw. In fact, it is quite common to do so. I use an 8 inch stack on my Delta contractor's saw with no problems, and before that, I used an 8 inch wobble dado.
You certainly would not want to use a 12 inch blade on a 10 inch saw, as that large of a blade might have clearance problems as it is adjusted. Use of a larger blade also causes somewhat larger tip speeds, so that might potentially cause problems. (Unlikely, but possible, since the differential in tip speed would be only 20%.) Perhaps these issues are what the author meant when they made that statement.
In going to a smaller blade diameter though, the only question is whether that blade will be able to reach the surface of your table. On an 8 inch blade there is no problem.
For what it's worth I've used a 6" stacked dado set in my small 10" saw for years without any issues. My understanding is that dado blades should always be smaller than the saw's rated blade size due to the increased load of cutting a wide dado over just cutting a saw kerf width. The smaller diameter means your saw will be able to exert more force on the teeth than it would with a larger diameter blade.
Are you sure the blog you saw wasn't referring to not using blades that are larger than the saw's rated size? I could see issues with that but I'm not sure what the problem might be with using a smaller blade.