Have never had porcelain tiles but I will say ceramic tiles don't really chip very easily
It depends on the tile, and on if the tile is set correctly.
In general porcelain is stronger than ceramic, but ceramic tile comes in many grades, and some are industrial in strength (see Jack's thread).
What are folks doing about protecting the grout from chemicals and staining? Is some grout more resistant to that than others? What are the pros and cons of narrow or non-existent grout lines?
With cementitious grout, yeah they make sealers. YMMV
But nowadays grout technology has changed a lot. Epoxy and urethane grout have changed the game in terms of grout performance. Yeah, they're expensive, but they are completely waterproof and impervious to chemicals (once cured).
Both take some extra skill in working with them, and epoxy grout sets fast, so you need to work in small areas. The cleanup is also kind of complicated (epoxy grout is cleaned with a diluted vinegar solution, and excess MUST be cleaned completely, or else the haze will really stick to your tiles).
I was VERY happy with the last DIY job I did with epoxy grout. It's not that hard to do, but you need to read and follow the instructions closely, because it is quite different from conventional grout.