In this case you ought to say "there is an order of magnitude more software available...(base Y)".
Otherwise, using your argument, for the same numbers you could equally say "there is a constant factor more more software available", in that for X ARM apps there are X*c x386 apps for c > 1
Obviously this is true for the constant c = X^(Y-1)
As soon as you start playing with two constants, there is an infinite number of functions that can interpolate between them (and hence describe their relationship). This includes exponential functions, polynomial, constant, sinusoidal, linear...