The G.I. bill is not a tax on the civilians, members pay in and receive the benefit after 2 yrs service as i'm sure your aware. But the G.I. bill system is not 100% utilized,  a lot of the costs are paid by members who do not use it or choose to use it for certifications instead. 

I have never received or seen discounted housing for vets? At the most i've seen a preference for vets because we tend to leave the property in the same if not better condition than when we left it. 

The retirement is a federal benefit that all federal employees get. That state offers retirements, as do many companies for members who put in 20+ yrs. 

The discounts bring more customers, companies actually make money for imposing discounts to state, federal, disabled, seniors, and vets. 

In the end, i see it all as an appreciation for volunteering our life and livelihoods when we could have made a lot more money in the civilian world. Most of our skills don't transfer to the civilian sector, we start from 0