"We only got along for how many hundred years without epoxy grout?" We only got along for how many thousand years without indoor plumbing of any kind? Do you want to go back? We only got along for how many million years without electricity? Do you want to go back? In 2010, we have epoxy grout; the materials cost is commensurate with the materials cost for cementious grout, but epoxy grout does require more care to install than cementious grout does. In damp environments, epoxy grout is hands-down superior to cementious grout; it is much less hospitable to mold and mildew than cementious grout, and is easier than cementious grout to clean when mold or mildew does gain a foothold. There are lazy tile installers who just want to get in and get out, to charge the customer to install the tile; but they do not want to be bothered to use superior materials that would make for a superior finished product if it requires more effort on their part. Those lazy contractors should not be encouraged or humored.

So, as several people have said, you don't use grout at the tub or floor/wall junction. That end wall tile around the rounded edge is really bad. They used a dull bit to cut (nibble) and it looks really amateurish. It's not really clear what's going on with the edge, but it doesn't look like a properly finished edge (with a bull-nose tile). There's obvious grout / adhesive left on the surface. I think they used sanded grout - and that's why it's so rough and not filling the voids properly. My guess... is that the overall issue is that these folks didn't know what they were doing -- which is likely a bigger problem than just the cosmetic issues. I think you will find problems with the waterproofing under the tile also.

If you have a curb, you will have the cracks develop there, too. and where the walls meet the floor. Anywhere where two different materials meet or where one surface meets another that is in a different direction (known as "change of plane"). My contractor still grouts such places, too. But I did a solid surface shower that he could not do wrong. I am keeping an eye on the place where the floor meets the shower pan, all other places are in dry areas. So there it is just cosmetic. I would guess that water can get behind your tile with those cracks. If properly waterproofed it is fine, but if not, I would get to this as soon as you can. A lot of shower builders do not use waterproofing, even though it is now required. If you do a search on this forum for "Shower waterproof," you can see many discussions about it and learn what is and is not waterproof. (Redguard yes, Durock no, for instance.)

Hard to know for certain, but these problems are commonly associated with two things: overwatering and mixing too fast. Installers are especially prone to these mistakes on modern fast-setting grouts - it's tempting to add water and mix fast because you're running out of time and the grout is stiffening. Unfortunately, that results in problems worse than having to mix up another bag.