It's likely that Steve Jobs is donating anonymously.
It's actually a more efficient use of time. You can focus on your specific interests, cut a few checks and say, "keep it quiet." Once you donate publicly, you have to fend off other organizations asking why you won't donate to them.
Knowing Steve's personality, it's perfectly credible that he has implemented a "no-tell" policy for charitable contributions for optimum efficiency. It keeps things elegantly simple.
It's also likely you are talking out of your a** with nothing to back you up whatsoever.
Sure, an ego-maniac like Jobs would do something anonymously. Just like he gave Woz all the credit for actually building the computers and writing the first ever GUI.