The iPad was the elephant in the room as Gartner and IDC reported that worldwide PC sales in the second quarter of 2011 were even worse than their modest expectations.

Shipments grew only 2.6% according to IDC and only 2.3% according to Gartner, well below the 6.7% Gartner had predicted and a fraction of the 12% IDC reported in Q1.

Apple, by contrast, registered an 8.5% or a 14.7% bump domestically, depending which report you believe.

“Given the hype around media tablets such as the iPad, retailers were very conservative in placing orders for PCs,” wrote Gartner’s Mikako Kitagawa.

IDC’s Rajani Singh attributed Apple’s competitors’ weak results to several factors, including a “hangover” from last year’s 20% growth, the “ongoing contraction” of the mini notebook (e.g. netbook) market and “consumer interest shift[ing] to media tablets.”

Both tracking firms include netbooks, but not tablets, in their PC totals, but at least they now acknowledge the oversight in their footnotes.

Even without the iPad, Apple (AAPL) has become the No. 3 vendor in the U.S. after Hewlett-Packard (HPQ) and Dell (DELL), and it continues to gain on its larger competitors. As Gartner’s press release put it:

“Based on preliminary results, Apple showed the strongest growth among the top-tier vendors in the U.S., as it climbed from fifth place to third, overtaking Acer and Toshiba (see Table 2). The preliminary findings show Apple’s performance far exceed the industry average, partly driven by an iMac refreshment that attracted both consumers and buyers in the education sector.”

Below: Gartner and IDC’s spreadsheets for the U.S. and worldwide PC markets.