There is a different between sealer and curing compound. Curing agents are applied while the concrete is uncured, to retain moisture and prevent the surface dehydrating and therefore hardening faster than the underlying concrete, which causes cracking. One of the common ones is a latex based liquid which seals the surface temporarily, breaks down in UV light and disappears in a few days. Sealer is applied at least several days, if not weeks, after the concrete is poured, and is used to enhance the appearance of the concrete, prevent staining and to try to keep the colour as uniform as possible under wear and tear.
As for the cracks, they have occurred exactly where they were intended and as others have said, the tooled joint probably should have extended around the lip. In saying that, the crack would still occur so there is no structural or functional failure, purely aesthetic, and even then minor. I doubt it will get any worse, and I think you'll find in time you will barely notice them.
Where they have saw cut, did they use a continuous rim blade, or a segmented blade? Continuous rim will cause a lot less spalling along the cut. If you really need it fixed, it could be caulked with a coloured urethane caulk.
FWIW, I am a structural foreman with a concrete/formwork company in Australia.