Ree, comics were always considered a poor form of writing (and often they deserved the reputation, the writing was basic and done fast because comics were pumped out by the hundreds per month)
There are graphic novels that are very text heavy, there are those with almost none (such as Matt Phelan's GN's)
I love a well conceived wordless pic book, it allows a child's imagination and creativity to be put to task. I'm thinking the trend to fewer and fewer words has to do with what was said earlier, the target age range seems to have been lowered as more 6 year olds start into reading chapter books. At a round table Q&A a few years back a well respected Agent on the panel said the age for pic books is more like up to 4. The two Editors chimed in saying they felt it was more like up to 6, but the agent may be right, that 4 is probably the age where BUYING pic books peeks and lessens after that. I know my granddaughter is getting out of pic books, as she is just entering grade 1. They still enjoy them at that age, heck so do I:) but parents, grandparents are probably not buying them as gifts etc.
At 3 and 4, too wordy pic books can loose an audience. I read one book that was around 1500 words once and saw 3 and 4 year old kids laps into a comma:)
If the art is too simple (not enough detail to keep them looking as you read) and the words too many, the child often times starts turning the page before your finished. I think higher or lower word count just depends on the style of art used, the subject matter, as to if it works or doesn't work.