So far, all the Internet information I find lead me to think that all Glocks come with a recoil spring that is roughly 17lbs of compression weight. Is that true?

In the G3 Glocks the full size use a 17# spring, the mid size use a 18# spring and the compacts use a 16# spring. On ths G4 Glocks they have changed several times and have not advertised the spring weights.

So a gen3 Glock 17 shares the same compression as the more powerful gen3 Glock 20? And if so, are some springs progressive and some linear compression?

All G3 springs but the subcompacts are of the same design. 16# G26/G27/G32. 17# G17/G17L/G34/G20/G21/G22/G24/G35/G31. 18# G19/G23/G32.

I would think that the slide mass is less with bullet energy being the same in the smaller slides. Therefore, slide velocity will be greater with the smaller slides. To compensate, increased spring strength is required. JMHO

The sub compact with the smallest slide has the lightest springs so who knows other than the Engineers who designed them.

Supposedly early 9mm Glocks used a 19lbs recoil spring, I'm not sure which models that includes but it's likely the Gen1's and possibly the earliest Gen2's. According to Wolff: 17lbs: 17,17L,20,21,22,24,29,30,31,34,35,36,37 18lbs: 19,23,32,38 16lbs: 26,27,33,39 I don't know what the Gen4 weights are, I know the Gen4 sub-compacts have the same weights as Gen3. I don't know if the .380 models use the same weights as 9/40/357/45GAP.