I think that quote holds less and less true over the years.  It's not so much that there are huge numbers of people who need their PDEs solved, rather that those who do (aerospace, engines, circuits, oil, climate, defense, energy) <i>really</i> need them solved and are willing to pay for it.<p>One thing I enjoy about PDE solvers is that algorithmic improvements always pay off because <i>every</i> user is running the largest simulation they can on the most expensive hardware they can afford.