me too ! here are the reasons
1. cutting, most porcelain tiles are considerably harder to cut than ceramic and genrally larger format therefore require different tools than
standard ceramic tiles,these are more expensive than the bog standard ceramic cutters and some porcelain cant be cut on a slide cutter and needs to be wet cut therefore more time consuming ,time is money
2. drilling as doug said drill bits dont last long and are pricey and you cant use a hole boy on porcelain
3.rectified edges are more unforgiving than the cushioned edge of a ceramic
tile and I would argue the standard of your work needs to be higher on porcelain work
4.special adhesives and grouts,all the adhesives and grouts will need to be flexi and flexi adheives are more expensive