"The customer lists all the features they want in priority order."

And how often can your customers tell you exactly what they want, let alone as a prioritized list?

If you are lucky enough to get a feature list, and it doesn't change half-way through, everything will be top priority. If you make the decision for them, you can bet you'll make the wrong one - whatever you choose to treat as low-priority will be the one thing they really, really needed yesterday.