The blood prohibition only remains because the WTS cannot give it up completely without looking like a bunch of idiots and, more to the point, risking opening up a host of legal claims for compensation. Ultimately EVERYTHING in the WTS comes back to money.
They have created a maze of logical nonsense to give Witnesses as many options to take blood as possible to try and minimise the risk of deaths and the associated bad publicity.
They have got caught trying to water down an edict that really they can only interpret with a fundamental bias that they are not prepared to stand by.
Sure they stick to Biblical texts as the basis for the prohibition (which is more than they do for the generation explanation) but it would be naive to think the continued arbitrary position on whole blood and the four so called primary components is any thing other than a compromise to suit organisational policy goals.
They have the similar issues with 1914 and the generation interpretation.