Gibson is an excellent writer, but we all know that he wrote his first four books on a typewriter. The book is set in the future, a very indeterminate future for about the first third of the text. We eventually find out that we're talking about 2005. The plot revolves around the aforementioned killer. The reason for this is fairly simple.
Spikes can reach high voltages.
They can also bypass the protection of fuses and many simple types of surge protectors. The reason that spikes can get through to flip bits in memory is that they are transient. Being of such short duration, they don't have the power to blow fuses. Since they can't even blow fuses, they certainly wouldn't be able to charbroil a user. Even if a spike could get through with enough power to do any damage, the ability to hurt the user would be very hardware dependent.