Are you generally asking why a couple could live on one salary in the 60's/70's and not these days? If so then It's all a matter of lifestyles: reason number 1) people are reaching higher on the property ladder than they used to - often not by choice i would add which means the proportion of your salary that is spent on mortgages, has increased 2) holidays are abroad by majority, rather than in the UK by majority 30 years ago and thus a hell of a lot more expensive 3) price of living goes up as people's tastes change; foreign/exotic food - shellfish for example - is more commonplace on the weekly shopping list not a once-in-a-blue-moon treat that it used to be, also take-away food is more commonplace, entertainment through sky/cable/internet/computer games consoles etc 4) public transport is in the minority these days with most families having at least one car (sometimes 2), whereas people used to use buses/trains more predominantly in the 60's/70's. there are many many other lifestyle differences between now and 30/40 years ago but i only have 2000 words.
Yes there was a marriage allowance but not a vast amount and certainly not really an incentive to get married (which was one reason why they scrapped it).
Price comparisons is very difficult as the price of living has changed so much in the last 4 decades - the average house price in the early 70's was around �2000 - �8000 for example (if only they cost that now!)
And finally, yes Mrs Vader is a housewife, by choice, she is a qualified teacher (taking a year out to be with son number 2), and though the 2nd income (especially a teacher's salary) would be very nice, we're doing quite well on one salary.