Attention holiday shoppers: online merchants are planning to make it really worth your while to buy stuff from their websites this holiday season. That may not be such great news for investors, though.

As the Wall Street Journal notes, the offers will include free shipping, online-only discounts and gift wrapping, a skill I have never mastered. The news isn't that these offers are available, but that more of them are coming. Even with the worries about overall holiday spending, online holiday spending is expected to rise 21% this year to $33 billion, the paper said, citing data from Forrester Research.

Though this is great news for consumers, it underscores how worried retailers are about the holiday season, which most pundits expect to be lackluster overall. High gas prices also may keep consumers away from shopping malls.

That's good news for the likes of Amazon.com (NASDAQ: AMZN), which is offering Black Friday deals for the first time, and eBay (NASDAQ: EBAY), which is offering free shipping on some goods. Bricks-and-mortar merchants are already getting the message.

Wal-Mart (NYSE: WMT), which had been in Wall Street's dog house for quite a while, is well-aware of these trends. The world's largest retailer surprised Wall Street when it said that its decision to start discounting two weeks earlier than usual paid off. The company's quarterly profit rose more than analysts' forecasts, and it boosted its full-year outlook. Though shares have jumped the most in five years, they are still down for the year.

Further crimping the profits of online merchants is the rising popularity of comparison shopping sites such as Shopzilla. For instance, I found prices for the Nintendo Wii console ranging from $329 to $650, so it pays to comparison shop. That's great for consumers but bad for merchants because it ratchets up price competition.