What are you talking about? Old game had his chances too. They are there FOR THE PLAYER, not the soldier. And a soldier would have a rough understanding on how likely is to hit someone under different conditions
No it didn't actually.
Xcom UFO Defense gave numbers for weapon accuracy.
Xenonauts gives numbers for chance to hit.
In Xcom UFO defense you're given an accuracy number which reflects the relative ability of your soldier to fire that gun. When you fire the accuracy determines how much the shot can deviate with lower accuracy resulting in much higher deviation. Even if you have 100% accuracy you can still miss the target.
In Xenonauts you're given numbers for chances to hit individual targets. You're also given the in-game formulas in the manual which detail percentages for each individual action, ranges, cover etcetera to encourage the player to maximize his manipulation of those numbers. Aiming is even incremental allowing the best maximization of those chances. The numbers are absolute and when you fire you hit or miss based on those numbers.
And what is the end result?
Xenonauts is a hit/miss calculator. If you miss your shot is going to go some random place within a certain cone of fire. What this means for example is that if a target is behind cover, the manual for example lists a box, then the odds of hitting that target decrease by 40%. But if you miss because of that 40% shift that doesn't mean you'll be hitting the box. It just means you'll not hit the target.
XCOM meanwhile the accuracy changes the cone of fire. So taking that same example, if the target is behind a box then the cover decreases the chance to hit that target because it literally makes the target smaller. You can have a shot that deviated lower and would have hit the target's legs hit the box instead. It's readily apparent that hitting the box prevents your shot from hitting in XCOM, but in Xenonauts that 40% reduction to hit just results in the shot going to a random location and you may never hit the box at all.
Also in XCOM if you're a long way from your target and at 80% accuracy there's a lot of room for deviation and you have the potential to miss by quite a distance. But if you're closer that same degree of deviation may not have the same time and room to grow so a shot that would miss at 80% accuracy at long range will now hit at the shorter range or it will miss by less.
So the two games are VERY different in how they handle combat both in how it's presented to the player and in how it actually functions within the game. XCOM uses radians, that is the computer shooting a beam at one target from another within the game and creating degrees by which that beam can deviate whereas Xenonauts is simply hit or miss. Xcom gives the players numbers on the soldier's ability to fire certain types of shots given their condition whereas xenonauts gives the players numbers on the soldier's ability to hit a specific target in a specific circumstance. Xenonaut hit chances are exact numbers, Xcom's accuracy numbers are relative ability.
Or put another way, Xenonauts is a game of absolutes, Xcom is a game of degrees.