Some odd things

[Strike]

Actually, a plausible answer to both:

At no1 :RoF has a much simpler engine and damage models (they simply have fewer systems than world war II aircraft and would be like comparing a VW Golf to a Bugatti Veyron). So I would imagine they can devote extra resources to simulating the breaking of wings and having that hit the other planes. On another note, RoF does not model much other than wing and control surfaces falling off. Il-2 models pieces of the fuselage that can fall off (engine nacelles/tail sections etc.). Another thing I've noticed a few times in RoF is that you don't always get hit by these parts, even if you fly through them. It seems a little random to me sometimes. RoF also has much simpler fire damage than Il-2 CoD. Fire starts and slowly kills pilot unless you dive at a speed near structural limits to put it out. In Il-2 fire now spreads depending on speed and other things. I've seen fire work it's way from my wingtip to fuselage in a He-111. That was some scary stuff...

So short summary : A lot of stuff CoD models, RoF would never take advantage of (advanced systems even such as landing gear which consists of hydraulic/pneumatic systems, pumps, hoses, pistons, mechanical locks even tires).

That must eat some resources.

and on question no 2:

Trees in RoF used to be buggy imo. Seemed that you could fly through a cluster of trees and visually not hit anything, but still get "caught" in something (even though the replay shows 10-20 M from plane to nearest trees. The forests in ROF are so dense they could really just be a huge hitbox (much like original IL-2, just not insta-explode) with some random "heights" modeled. I am not sure, but my thought is that when crashing in seemingly thin air, the surrounding trees have a larger invisible hitbox to sort of "cover" many trees.

And compare IL-2 CoD viewdistance + RoF viewdistance and look at the RoF terrain compared to CoD terrain. CoD does have much more object population, not to mention trees than RoF. Trees in RoF also look much bigger (some look like 10-15 meters tall) whilst trees in CoD seem much smaller in general. The amount of "flagpole" hitboxes you would have to model and update constantly for each single tree on the map would be resource draining. That's the answer the devs gave too.

I hope this clarifies a few things