DDI has allowed me to not buy books as well... I probably would buy the books if my financial situation had not downgraded...that is all.
Unfortunately, I'm in teh same situation. Because of recent developments, I have to tone back on book purchases. Since I've already got DDI, I'm not really all that concerned. Works out pretty well actually.
I pretty much buy books either right away or not at all. Every time I need something from adventurer's vault, I just look it up in CB. Not as easy, but makes that 60 dollar investment all that much stronger.