My observation, not just from this forum but from several other sources, is coolant failure is the leading cause of premature engine failure. Your cooling system won't necessarily blow up but the internal corrosion leads to hot spots, warped heads, failed head gaskets, etc. For that reason I do a 'drain and fill' every 2 years on all my cars. With that service interval I'm perfectly happy with the cheap green stuff. Twelve dollars of coolant and distilled water plus 15 minutes of time is cheap insurance. For the manufacturer with their long warranty spending extra on fluid saves them warranty expense on fluid changes. If I was to try and go to a 5 year change interval I would spend more on fluid. But then again the reason I don't do that is I still don't believe the 'lifetime' fill claim. BMW claimed that with ATF years ago and we know how that worked out.