Yes, definitely take that 70% number with some skepticism as who is pushing that number. (Investment advisors, banks, mutual funds, etc make more money the more investment assets you hold as they get a cut through management fees off 1 - 3% of the asset value regardless whether they make money for you or not). I've seen it being quoted up to 80% (RBC for example) so people are discourage from actually retiring and keep on saving and working, which is ridiculous.
Often time people parrot what is suggested in the US as if circumstances are the same in Canada. That 70% number might be applicable in the US, as their Social Security system is so underfunded and about to run out of money by 2035 plus their health care system is so pitiful that many are uninsured or under-insured because it is too expensive, so in the US people have to save a lot to cover their retirement years. In Canada, the CPP is well funded and in good shape for the foreseeable future plus we have universal health care so we don't have those two big worries.
So what percentage of your present income do you need on retirement? That wholly depends upon what your retirement plans look like and what standard of living you want. The average Canadian with $80,000 (family income) spends approximately this:
Annual Family Income 80,000
RRSP (6.5%) 5,200
Child raising costs 10,000
Mortgage payments 14,000
Employment expenses 3,700
Taxes and MSP 9,600
Income left over for consumption (42%) $34,000
All or most of those cash expenditures (except taxes which would be reduced) would be eliminated when you retire. Everyone's circumstances will be different as some may have already paid off their mortgage and other may not. So, it is actually closer to 50% of your pre-retirement income than 70%. That is the cash expenditures if you want to maintain your current standard of living (i.e. the same discretionary spending).
There is a real nice article from MoneySense magazine Retirement: A number you’ll love about this misconception about how much you really need to retire.