I've always wondered why HTC chose to only model the low altitude 109's.
I don't know. I am curious as well.
Was it that the G-10 used to fill the place of the earlier high-altitude 109's in scenarios?
No, it really wasn't a Bf109G-10. It was a Bf109K-4 with the same exact performance chart as the Bf109K-4 has in AH right now, top speed of 452mph and all. In AH1 HTC simply called in a Bf109G-10 so they could put 20mm and gondola option on it. In AH2 they decided they wanted a greater degree of accuracy so they removed those options and correctly labeled it a Bf109K-4.
There really has never been a high altitude Bf109 in AH. I really hope that gets addressed someday.
Once the AH1 models have all been updated I would like to see the "core" (i.e. famous) WWII aircraft get updated from their older AH2 models to current levels. I'd consider the B-17, B-24, Bf109s, Fw190s, P-38s, P-47s, P-51s and Spitfire to be those core aircraft. That would be the ideal point to see some additional models added such as the frequently requested A-36, B-17F, B-24D, Bf109E-7, Bf109G-6/AS, Bf109G-10, Fw190A-3, Fw190A-6, Fw190A-9, P-38H, P-47C-5, P-47D-23, P-51A, Seafire Mk III, Spitfire Mk II and Spitfire Mk XII.