This thread is deteriorating pretty fast, but as someone who rides both modern and vintage derailleurs and IGH, maybe I can help clarify some of these points.

Like a single-speed or an old long-chainstay 5-speed derailleur setup, the chainline of an IGH allows using a chain with full bushings, the same sort of chains used industrially for far longer lives than any bike chain. A full bushing has many times the bearing surface of a derailleur chain, and in better full-bushing chains, the bushing is an alloy chosen for lubricity and wear resistance without needing the tensile strength of the side plates. Finally, the full bushing holds lubrication better against wash-out. So, while they don't last forever, and do have friction, it's not unusual for a full-bushing chain with a chainguard to last tens of thousands of miles.

The wear issues of smaller cogs are more complex, but have to do with the greater angle of articulation of each chain joint as the chain moves around the cog, as well as the greater load per joint on smaller cogs. Similarly, the angled chain lines of modern derailleur systems stress the chain joints while they're articulating, creating greater friction and wear than the same chain on a straight chainline.

If you're really interested, your local library may have a copy of Mechanics of the Roller Chain Drive for the math behind the greater friction and wear of small cogs and angled chainlines.