Sorry, don't like it and find unrealistic.
If you have experienced troops available AT ALL, why can't I use them to reinforce a weakened unit (i.e., <10)?
In SC:ETO you could actually have experienced units. I liked how it worked, even if it represented an "infinite" pool of experienced replacements.
Part of the reason you pay extra for elites, presumably reflects their limited availability.
In a real sense, a unit that has 10% experienced veterans and 90% "green" troops is a *lot* more effective than a unit with 100% green troops. The game appears to model it as a linear dilution of effectiveness (i.e., replace 5/10 troops - lose 50% of experience).
Other mechanism could be easily created to model the fact that even a small cadre of experienced troops bring enormous benefit. Simple one is to carve out a portion of the experience base that is unaffected by the replacements:
Example:
New experience = 0.6 * old_exp + 0.4 * old_exp * (old_troops/total_troops_after_reinf)
In game terms, the inability to replace losses (vs. only over-strength) with experienced troops means that there is little point in the game system that allows for experience. Virtually every unit will be "0" or "1" at best. Only units that experience virtually uninterrupted luck (high enemy causalities AND low self causalities) will ever grow in experience.
If you wanted to have a more "realistic" system, you could have every country have a small generation pool/turn of elite reinforcements (e.g., Germany 8/turn) and then add in a fractional loss for each strength point lost in combat (e.g., 1 per 5). Then get rid of the increased cost, since you are handling the limited availability in a different way.
Sorry, but I just don't buy that my veteran troops are un-employable and unwanted until my army decides to over-strength some corps.
-brett