Ray brought this to my attention on Twitter. It seems there's an incompat or bug with <cfdump> / writeDump() when it comes to how the TOP attribute works.
Repro case here: https://gist.github.com/adamcameroncoldfusion/6257903
On Railo TOP only seems to impact array & struct's level-nesting depth, which it does the same as CF. However on CF - and the intent - is that it also controls how many rows displayed with queries and arrays as well. Run the attached code on CF and Railo to see the difference.
My interpretation of the Railo docs is that's what's supposed to happen in Railo too, hence suspecting it's a bug rather than a purposeful incompat?
I'll raise a ticket once we confirm whether we count it as a bug or an incompat.