Shares in Apple Inc. closed above the US$400 mark again Friday, its first trip into such rarified heights since July 26th, when the stock set at an all-time closing high of $403.41 and an all-time intra-day time of $404.50. Friday’s close was $400.50, a gain of $7.54 (+1.92%), on strong volume of 24 million shares trading hands.

Near-record closings aside, Friday’s closing high represents a $26.78 gain since August 25th, the first day of trading after Steve Jobs announced he had stepped down as CEO from his company. That represents a 7.2% gain in approximately three weeks, an impressive feat for any stock, but even more so considering the angst that had surrounded Steve Jobs’s possible departure in the months and years leading up that event.

Three month chart for AAPL from June 16th, 2011 to September 16th

Then again, it is likely an aspect of those months and years that has allowed investors to be so sanguine about the change in leadership at Apple today. Wall Street had plenty of time to cope with the reality that Steve Jobs would eventually have to step down from the CEO role, and his previous absences from the company provided what Changewave Research recently called an “inoculating effect” against that departure, though Changewave was referring to customers and we’re talking about investors.

Source: Changewave Research

Nevertheless, the research firm has surveyed people for three years on whether or not they would be less willing to buy Apple products if Steve Jobs left the company. That number began at 18% of respondents who said they would be less willing to buy an Apple product without Steve Jobs as CEO, and it sank to 4% during the course of those three years, as you can see in the chart below. Wall Street appears to have taken a similar path as consumers.

The broader markets also enjoyed a rally today, with all three major indices closing higher.

For those keeping score, Apple’s market cap is now $371.3 billion, keeping Apple the world’s most valuable company. Exxon Mobile, the world’s second most valuable company, also closed higher at $74.55, up $0.54 (+0.73%), with a market cap of $362.5 billion.

*In the interest of full disclosure, the author holds a tiny, almost insignificant share in AAPL stock that was not an influence in the creation of this article.