pay for only what they need today is often cheaper than spec'ing out beefy hardware to handle tomorrow's scaling issues....plan for a small monthly expense vs. huge up front expenses

this is probably the biggest "value" in cloud infrastructure. Capital expenditure is difficult to obtain, but debt is both easier to obtain (esp. in such low interest rate environment of today), plus debt is tax deductible immediately, while capital expenditure is at most a depreciation over the expected lifetime of the hardware.