Numbers like , (b / CDM), and Q are determined by physics as surely as the He and D abundances - it's just that the conditions at the ultra-early eras when these numbers were fixed are far beyond anything we can experiment on, so the relevant physics is itself still conjectural.
The inflation concept is the most important single idea. It suggests why the universe is so large and uniform - indeed, it suggests why it is expanding. It was compellingly attractive when first proposed, and most cosmologists (with a few eminent exceptions like Roger Penrose) would bet that it is, in some form, part of the grand cosmic scheme. The details are still unsettled. Indeed, cynics may feel that, since the early 1980s, there've been so many transmogrifications of inflation - old, new, chaotic, eternal, and open - that its predictive power is much eroded. (But here again extreme cynicism is unfair.)
We'll be hearing some discussion of whether inflationary models can ``naturally'' account for the fluctuation amplitude Q = 10-5 ; and, more controversially, whether it's plausible to have a non-flat universe, or a present-day vacuum energy in the permissible range. It's important to be clear about the methodology and scientific status of such discussion. I comment with great diffidence, because I'm not an expert here.
This strand of cosmology may still have unsure foundations, but it isn't just metaphysics: one can test particular variants of inflation. For instance, definite assumptions about the physics of the inflationary era have calculable consequences for the fluctuations - whether they're gaussian, the ratio of scalar and tensor modes, and so forth - which can be probed by observing large scale structure and, even better, by microwave background observations. Cosmologists observe, stretched across the sky, giant proto-structures that are the outcome of quantum fluctuations imprinted when the temperature was 1015 GeV or above. Measurements with the MAP and Planck/Surveyor spacecraft will surely tell us things about ``grand unified'' physics that can't be directly inferred from ordinary-energy experiments.