At the bottom line therefore the rise in the value of labour is merley one stepping stone in the over all devaluing of labour, as machines becoming increasingly important.
And yet haunting Marx ideas are two further points not explict, but implied here.
Firstly there is no real natural limit on what can be produced. If after all humans are really using the powers of nature to produce, what those powers can make, and how humans can use it is flexible: newness therefore tumbles into the entire scheme at every opportunity. New machines are endlessly being born, machines then then makes use of labour. The capitalist's system is also often (but not always) in need of labour. It can always do more (it has implied virtualities) than its population money and people for. It is after all tricky question. What rises quicker, the population (with is explontenial expansion curve) or ideas with God know what factorial expansional curve.
Marx therefore implies that ideas and the machines they create, tumbling from the skies, might always change everything, and keep a living poplation (and its labour) always valueble.
They might... So long as the options remain real and open. This is of course the horror in the climate change argument. The argument is that there really might be a natural limiter to things - a point or a timescale to change. A place where change becomes difficult from or next to impossible.
This in turn feeds into the second concession Marx implicitily makes. In a world where money is always relative, one might always gamble of the future. That is, one might found part of the system, at least, on the punt that ideas will always outstrip the population's labour capacity. If this is true then the economy will of course alway expand. Any debt one has now will (even given interest) naturally lessen with time. It will be more able to be paid as the economy expands.... one can therefore bet agianst this expansion, and include it within the over all picture.
This betting on future expansion, will then further mitigate the apparent harshenss of capitalism (or will for a group of people in the west -for the lucky ones). The future is a bright presence, a point to gamble with.
From which perspective the recent credit-crunck cum peakoil, cum environmental scare cum depression cum recession makes some sort of sense. The moment we stopped trusting in the role of ideas to answer any and every emergency, then entire enterprise collasped.
States felt they had to step in to give us some kind of future (and got caught up in the over all mistrust, or a least did in Britian), and here we are.
We now face the problem- what do we really think about those futures? Are we going to bet on ideas again? or global iron necessity (and so risk revolution). Captialism has no choice It must choose the former or risk that other brain child of Marx coming to the fore again. The twin problems we then face are a) do we agree with this equation and b) if we do not agree is there very much we could do about it?
A problem for genuine revoltionaries everywhere....