The same is true for a cell phone. Open one up, take out the board, remove its components and pour them back in the case. If you think the phone will work, I suggest you go into politics. Designing complex pc boards is like chip design, only on a different scale. Some of the same problems that plague chip designers are present in board design too.
Signal integrity is a huge concern.
In fact, a pc board is no longer a passive vehicle for mounting components. Once a board is integrated into the end product, it becomes an active component. To accommodate the increased layer count of complex boards and miniaturization pressures, designers resort to thinner substrate cores, which means thinner boards. Even with lower voltage on the chip and the board, the increase in horsepower from complex chips and boards means thermal problems. Complex designs are pushing the performance of FR-4.