I dont know, I've seen a consulting arborist picking and arranging flowers.
Also, the author has perhaps overlooked the problem when a tree crew billing some $300/hour with stump grinder, chipper and miniloader and the lady want roses pruned when in fact a gardener with a lawnmower could do that for a fraction of the cost.
You don't go to a micro surgeon specialist to get a splinter pulled from your finger unless of course there's something unique about it.
And finally, the treatment of shrubs is very different to trees, how often do you hedge a tree, or cut it back with secateurs for next years flowering like hibiscus?
That statement must have come from a typical academic. Am I right?