Serialism was certainly an influence on Cage's work nonetheless:
Most if not all aleatoric and minimalist forms of music are steeped in serialism - minimalism particularly took it to extremes with the uber-repetitive cell-like structures and drones in the music of composers such as Philip Glass.
At the other end of the scale, even the most random approaches tended towards event-driven serialism based on elaborate (or plain wierd and simple) sets of rules rather than the more parallel approach demanded by conventional diatonic harmony.
4'33" is, perhaps surprisingly, a good example of this. It has 3 predetermined movements. One movement occurs in time after another, creating a fundamentally serialized approach. The piece begins and ends in time, and in between, sound events occur. Some may be or appear to be "simultaneous", but most occur one after another. These are the works' primary features, and they are all serial in nature.
You could, of course, argue that the 3 movements exist simultaneously, or even overlap - but that does not take away the predetermined mathematical structure, it just makes it a bit more random - which is the "anti-serialist approach" at work, falling into the very traps it was seeking to avoid.
If you think about diatonic harmony, it is also fundamentally dependent on predetermined mathematically related chunks of music - except that the primary goal of the composer is not to organise these events mathematically, but artistically, and the mathematical nature of the music is usually a happy accident that the key relationships happen to fall into such patterns.
There is also a much higher tendency towards parallelism - multiple tunes or themes occurring simultaneously, greater concentration on harmony and harmonic movement, subtle dynamic and timbral changes. Formally, there is a great body of work in what appear to be pretty rigid formats, but upon closer inspection, most composers were pretty free with such apparently restrictive constructs as the Sonata Form.
With serialism, like Sonata form, the mathematical structure is key - it's the framework within which artistic exploration of the music can take place (if you're "inventive" about following the rules!). I found that you can create free-flowing jazz-like music quite easily using 12-note/serialist approaches, by manipulating the rules to suit the way you wanted the music to go.
But generally, the predeterimed rules are followed very closely - it's often said that Schoenberg was music's first beaureacrat.
I tend to find that having strict rules in place can lead to freer composition and artistic expression, and ultimately more rewarding music - and music written with few rules tends to be sprawling, overly abstract and hard to listen to frequently.
Could be just me, of course.