From the Wiki article you linked to:
Because the Roman Church had a virtual monopoly on its own history, its own Latin interpretations were considered sacrosanct, and as a result the Church's writings had rarely been questioned before. For Gibbon, however, the Church writings were secondary sources, and he eschewed them in favour of primary sources contemporary to the period he was chronicling
[snip]
Gibbon proved that the early Church's custom of bestowing the title of martyr on all confessors of faith grossly inflated the actual numbers. [my emph.]
[asbestos and kevlar in place]
Can you imagine what theology, especially apologetics (remember that "creation science" was originally described as a branch of apologetics), would be like if it adhered to the same standards as science: get caught lying once, you're out.
I read the "Decline and Fall" in its entirety off and on over the last three or so years. Extremely well written, but it drags in places; there's no way to make 1000 years of Byzantine emperors very interesting.
Very highly recommended. (Especially if you have a Latin dictionary handy to figure out the footnotes.)
I've read Gibbon and it took a long time, but it's not hard to see why it was controversial at the time. His description of the early church was quite objective and therefore rather uncomplimentary.
BTW, it's still very much worth reading. It's full of facts, so probably not for some of the crowd.