Michael Dorfman's comment on Stoicfury's answer is important, indeed for me it is the crux of the question, so I thought I'd expand on it.
'Simplicity', when applied to a set of rules, is an inherently meaningless concept. One might ask for example which is simpler out of the integers and a general ring- the former requires more axioms than the latter, but arises more naturally than the class of all rings: to say one is simpler, more likely a priori, would be wrong.
Occam's Razor works (at least, can be seen to work) because it is a statement in conditional probability: each additional entity X we posit to be at work adds another factor P(X¦ All the other entities posited so far) to our probability, each of which must be less than or equal 1. From another point of view, an additional entity occurs in a subset of instances, with lower of equal probability (by the monotonicity of probability measure [if A is a subset of B, P(A) < or= P(B)]).
Our problem comes from the fact that purely abstract entities cannot be ostensively defined- 'twoness' for example is a property that varies in its sense (if I break something in half, is that one or two?) and so their instances are not well-defined, making subsethood (and hence a priori relative likelihood) an impossibility.
We can rescue some semblance of a notion of likelihood, though, by positing the existence of entities which can be placed in ostensive correspondence with our abstractions: concrete mechanisms, for example, that produce the fibonacci sequence (or, more mundane, collections of objects that combine like the natural numbers under addition). And although it is somewhat surprising that such entities should exist, they most certainly seem to.
The OP cites a truncated fibonacci sequence and asks 'is the next likely to be fibonacci?'-naturally this depends on what our sequence is of (dividing cells? number of hats by size?) and the complexity of the mechanism he could propose by which fibonaccis should be produced.