I've noticed that, too. Perhaps a bad example, but the HUD on the F-15C in LO:MAC has a sort of 'slider' which shows the air speed, and indeed how fast you're accelerating. Not a steam gauge, but the principle remains the same. Makes it much easier to quickly attain a speed and hold it, as you can anticipate how quickly/slowly you need to accelerate/decelerate. The Russian cockpits, on the other hand, are awful for that kind of thing. Only the digits are seen on the HUD, and they only change in multiples of 10. So, 120, 130, 140, etc. Very difficult when it comes to managing your precise speed.