RcG
Pretty weird you can say 4+save has little effect...
8 bombers fly into a CAP of 4 fighters. 4 bombers survive.
Give the fighters a 4+ save, and perhaps 2 fighters survive, but the same amount of bombers are killed. Any additional damage must be done in subsequent ordnance phases, but it's too late because the bombers have effectively shotgunned.
Now under current rules 6 bombers and 2 fighters fly into a CAP of 4 fighters. all the fighters and 2 bombers die, leaving 4 bombers. You might as well have taken more bombers. However, give the fighters a 4+ save, and there's a 25% chance 2 bombers die, 50% chance 1 bomber dies, and 25% chance 0 bombers die. On average, 5 bombers are left, an improvement for the bombers over at present.