The argument is that, while they may not make much difference to the election result in 2015, they could do so in 2030.
The final paragraph gives a flavour of the argument:
Those who want the main features of our current student loan system to survive must ensure today’s students get at least as much benefit from university as their predecessors did. But that is a real challenge as higher education is no longer a small elite system reserved for a favoured few.