Variable annuities generally have guarantees, which are essentially just embedded options. To price and analyze these options you have to run large-scale Monte Carlo simulations. Many shops have >100K policies and are running 30 year Monte Carlo projections. You can imagine the computational power required, and the inherent parallelism of the solution.
Can you give more information on this? It actually sounds like an easy problem to solve to me.
Oh sure, it's completely solvable. In fact some companies have solved it, but most lack the expertise. E-mail me (address in profile) if you have any further questions.