U.S. blue chip stocks are sitting at levels not seen since late 2007 and within sight of fresh five-year highs after the Dow Jones Industrial Average (INDEX: ^DJI) extended its winning streak to six weeks. However, a rising tide isn't lifting all boats equally. A look at the S&P 500 (INDEX: ^GSPC) by Bespoke Investment Group shows that the number of components making new 52-week highs has been declining, despite the current rally bringing the index to levels not seen in years. The data indicates a relative lack of "participation" by small-cap stocks in the rally, which is weighted by market capitalization.

Home Depot (NYSE: HD) is one of the large-cap stocks that hit a new 52-week high last week. That's not the case, however, for home improvement competitor Lowe's (NYSE: LOW), which reported earnings this morning. The average observer might expect earnings from Lowe's to mirror Dow component Home Depot's better-than-expected report from last week, but that hasn't been the case lately. The company has underperformed consistently since the beginning of 2009, with same-store sales at Lowe's trailing Home Depot by an average of 1.8% per quarter. That continued today when Lowe's posted a same-store sales decline and lowered its full-year outlook. That underperformance and the resulting market share losses are reflected in the company's share price, which is up only 24% since the beginning of 2009, versus 141% for Home Depot.

Another of those big S&P stocks leading the charge higher is Apple (Nasdaq: AAPL), which reached all-time highs in Friday's trading. The move to $648.11 comes ahead of a key event scheduled for Sept. 12: the unveiling of the newest iPhone. Sentiment has also improved due to reports about the company's entry into the TV or set-top box business, but the more likely bonus announcement on Sept. 12 would be a new iPad model. The "iPad Mini," as it has come to be known, will sell at a lower price more competitive with tablets from the likes of Google and Amazon.

So is now the time to buy Apple, or are you too late the party? Learn everything you need to know about investing in Apple in our brand-new premium research report on the company. Inside, our top technology analyst goes through the must-know topics for an Apple investor. Better yet, we're offering a full year of updates to go with it, including his reaction to the iPhone announcement on Sept. 12, so click here to claim your copy now.