2jsminus1

Truth about concrete countertops? The only truth, in that link, is the goober wasted an entire year to finally settle on using the cheapest resin available. He called a professional that told him water based acrylics are his choice of sealer for countertops? Pfffttt
How long do you think 1mil plastic drop cloth would last being walked across vs 20 mil? Because 1 mil, of cheap plastic, is about as much dry film thickness that jack of all trades had protecting his tops.
Most people are just totally uninformed, and believe that days or even weeks of research will enlighten them on the miriad of products designed for specific needs.
It takes years of trial and error, coupled with research, to even start to comprehend all the variables involved designing in service coatings that will last.
Is concrete porous? Certainly, concrete poured out of a ready mix truck, or picked up from your local big box store, can be porous. If not properly treated, all things exposed to the elements, trafficed or used regularly will show wear or degradation.
Most concrete tops, done by novices, are poured rightside up and troweled by hand. It may appear tight as glass, but it is not impervious to staining. And slopping on a run of the mill sealer doesnt prevent its inevitable failure.
Typically, the problem lies in the stigma that concrete is cheap, and therefore using what should be used, to protect it, cant be justified. The price per square foot, to handcraft a concrete top can be more than granite. Done right, its worth the cost to appreciate its individuality just as any art.
But like anything else, if you want a solid surface piece of cement and aggregate thrown together, using readily available materials, then you get what you pay for.

Also, I'm not certain what brand or type of epoxy/polyurethane you used for your own tops, but I'm sure you're aware not all are alike. Those words are thrown around as if one manufacturer makes all others. Joe blow or even a seasoned professional, may believe that using table top epoxy and minwax polyurethane for concrete tops is suitable and all is well. Then, the next thing you know he's complaining to his neighbor how concrete just sucks arse!