The banks loan nominal sums not percentages.
Point taken, and this is why I think wage inflation must be taken into consideration...Unfortunately, it's not too easy to estimate this though.
The only really long term study I've seen on housing, the Herengracht Index, shows tight coupling between rents and wages, and looser coupling between the price of rents and the price of houses. This does suggest that house prices and wages align eventually but clearly there can be frothy times where they go out of sync.
If HPI runs ahead of wage inflation then the couple in the starter home may be in a better position to trade up than if they hadn't bought but they would be even better off again if prices stayed flat.
I think that this again depends on wage inflation compared to HPI. Even if HPI ran ahead of wage inflation, they could be better off in the rising market than in the flat one. I'll use two of the same scenarios as my last post, to try and explain what I mean:
<Flat market>
5 years have gone by, they want to trade up to the nicer house which costs 500k. Because of their equity of 20k, they will need to take out a mortgage of 480k. To service this over 30 years @ 5% will cost them 2,575 p/m. This would be around 40% of a combined annual wage of 77,250.
<Moderate increases in market>
Same story; after 5 years they want to trade up. This time houses across the board have risen by 20%, so they now need to pay 600k for the nice house. Due to the equity they've built up of 60k, they'll need to get a mortgage of 540k. A 30 year term @ 5% will cost 2,899. 40% of an annual wage of 86,970 would cover those payments.
While HPI has risen by 20%, the amount of wage increases they would need to buy the same house has not risen by such a high percentage. In fact 86,970 represents a 12.5% increase on the wage they would have needed to get the house in the flat market.
After looking at all this, do you still think that the blanket statement that it's easier to trade up in a flat market holds true? As far I as I can see in a flat market you're better off to rent and save up for the house you really want to buy. In a rising market then "property ladder" rules come into play and you get left behind if you're not on it.
BTW, I think that this excercise is mostly academic anyway. How often does a market just flatline for a long period of time in reality?