"which leaves the question of why the word of God got these Christians executed. It can only be because they were speaking about it, can't it?"
No, there are clearly other possibilities apart from speaking about the bible or speaking about God. It could also be becaue of:
~ obeying the word of God above and in defiance of what the government or apostate religious authorities say.
~ translating the word of God to make it available to all, in defiance of apostate church authorities.
So given that these other possibilities exist, it is wrong to take a very vague verse that simply says "the word of God" and make it very specific to "speaking about God" when that is only one of several possible reasons as to why they were killed for "the word of God".
When a bible verse is vague or lacking in detail and multiple specific interpretations are possible, the translator should preserve the verse's vagueness and leave it up to the reader to discern the multiple possible specific meanings. It is in my opinion, dishonest to mislead trusting bible readers into thinking the bible says something specific when it really does not.
A faithful translator sticks as closely as possible to the text and should not inject his personal speculations or explanations into the text. Who is he to correct the word of God? Did God make a mistake by not causing the inspired writers to be more specific? Did God appoint the translator to edit his word for him? Is the translator inspired? Contrast the great care that scribes took in copying the scriptures letter by letter, with the liberties that Watchtower and other sloppy translators are taking with the text. What Watchtower and others are doing is clearly wrong.