The Bible writers were unaware of any of these definitions. Blood was not separated by a centrifuge. Blood was simply regarded as blood. To contain some semblance of logic, the Watchtower should either allow blood use, or not allow it - in any form. If it wishes to disallow whole blood but (somewhat illogically) allow blood fractions, then all fractions should be considered acceptable, including red and white cells.
Common sense logic would indeed call for them to draw such a line, but they cannot. The organization painted itself into a corner in two ways: doctrinally, and legally.
The organization has attempted to carry forward its tradition of the blood ban while having to deal with the ever-growing complexities posed to them by medical science. With the recent distinctions between plasma, fractions, and components; there has been a dizzying attempt on the part of the GB to ban what needs to banned, and allow what can be allowed. This process has created a legalistic maze of do's and dont's for the rank and file. Did Jehovah not anticipate all of this when he directed the organization to ban blood? All of this pharisaical maneuvering on the part of the GB makes God look quite confused.
I believe that the bigger issue posed to the GB is that of legalities. The legal department has written a lot of the blood policy, and continues to try to sheild the Watchtower from lawsuits. What if the GB were to suddenly lift the blood ban? I believe that the judgements against the organization for past JW deaths would make the pedophile judgements look like pocket change. So, the organization has painted itself into a legal corner as well. The Watchtower's blood rulings and sub-rulings have created a legalistic fiasco that is nothing short of shameful.
Meanwhile, JW lives (particularly those of children) hang in the balance over this idiotic process of nit-picking and hand-wringing on the part of the organizational leadership. All of this is quite similar to the first century Pharisees' endless rulings and man-made laws which created a legalistic nightmare for their followers. The ruling body in Jerusalem has merely relocated to Brooklyn Heights.