£45K at 3% per annum gross interest equals about £810 after tax if you pay 40% to Uncle Gordon........ Even the extra £3k pension is worth £1800 after tax. Plus it becomes index-linked at 55 whereas the £45K justs sits there gaining not much income. Hence the advice being if you have an urgent need for the extra available from life commutation, fair enough - go for it. Personally I don't, so the higher pension rate is more attractive.
It would, of course, be an entirely different matter if risk-free 10% savings rates were still available!