The iPhone casts a giant shadow on the Web

Here’s a pie chart that should warm Steve Jobs’ heart.

That big blue slice covering 59% of the pie represents Apple’s (AAPL) share of the U.S. smartphone traffic in April as measured by AdMob, the world’s largest purveyor of ads on mobile apps and websites.

By the same measure, Apple also had the lion’s share — 43% — of the mobile Web traffic worldwide.

The point of the “AdMob Mobile Metrics Report” for April 2009, released Wednesday morning, was not to give comfort to Apple’s CEO. Rather it was to measure the large and growing shadow cast on the Internet by smartphones in general.

It cites a Gartner report that smartphones represented 12% of total mobile sales in 2008, and points out that those devices represented 35% of AdMob’s traffic in April — nearly three times their market share.

But Apple’s handheld devices — whose Internet shadow is more than five times their share — ended up dominating most of the report’s charts. Among the highlights:

Of the 7.5 billion AdMob ads displayed on mobile devices in 160 countries around the world, 2 billion were displayed on iPhones or iPod touches
The iPhone OS has only 8% of global smartphone market share, but generates 43% of mobile Web requests and 65% of HTML usage
In the United States, 20% of ad requests come from iPhones, 14.8% from iPod touches (globally, those numbers are 15.1% and 11%, respectively)
Apple’s share of U.S. ad requests grew 5.6% month over month
The iPhone’s share grew 3% in April; the iPod touch’s grew 2.6 [link]