Ouch...It kills me to hear what our customers consider expensive in telecom. Have they talked with an attorney lately?
The problem I see with the all cordless sale is what you mentioned: ease of use and features missing. Another thing is the cordless phones tend to get broken, or the batteries eventually lose the ability to keep a charge. The customer forgets to charge it one day and now it is useless, which by the way is your fault for selling him a system that he has to be somewhat responsible for. My experience is to always have at least one "desk" phone installed so if by chance the cordless phone is "wasted", they can still use their system. In any senerio, good and bad comes back to your inital consultation and reccomendation.