Forgive my ignorance, but what's the difference between the 228 & 229?

Originally, the slide.  P228 has the stamped/formed carbon steel slide.  P229 has a milled stainless slide.  The P229 slide is thicker and heavier.  Newer P229s have a hooked trigger guard and rail on the dust cover.

A good example would be 228/M11A1 as both are 9mm without rails or hooked triggers. Forget the enteral coatings, SRT, Short trigger, and engraving. What you have is the difference in the slides.
228 being folded and welded carbon steel with internal extractor.
229 has the milled stainless slide with external extractor.
Both models share the same size grips, frame internal parts are interchangeable but there is a small variations in the mag well.
228's were made in Germany, new 229's are made to the same specifications but in the USA.
228 slides will fit on a 229 frame.
229's in .40/357sig have a thicker slide then the 9mm models.

This.  Some prefer the P228 to the P229.  I own a W. German P228 but would love to have a P229 as well.  P228 would be my choice if I had to choose for no real reason either.

I have a German 228 and 229 elite. Both great guns. I will say the 228 warms up a bit quicker while shooting.