“It’s going to be a slow burn,” says Bart Decrem, CEO of Tapulous, speaking about the arrival of original apps for the iPad tablet computer that goes on sale this Saturday.

Decrem has a unique perspective on such things. He’s co-creator of the Tap Tap music game, one of the thousands of applications that flooded Apple’s (AAPL) newly-opened App Store in the summer of 2008. He was lucky; within a month, more than a million people had downloaded his game. By December it was the most popular free app of the year. It now generates in-app sales of nearly $1 million a month.

Most developers, by contrast, have lost money writing for the iPhone and iPod touch.

That helps explain the graphic, above, from a survey released Wednesday by Appcelerator, a maker of cross-platform development tools. It shows a 10 point fall-off in the number of developers who say they are very interested in creating an iPad app within the year, from 90% of those surveyed in January to 80% in March.

“We haven’t seen a lot of new apps,” says Decrem. “They’re not flying around like they did last year.”

In an interview with Fortune, he and Tapulous co-founder Andrew Lacy cite several contributing factors:

• A extremely crowded market. According to Apple, virtually all of the apps created for the iPhone — 175,000 at last count — will run on the iPad, although with pixel doubling they may not look so hot. “How is a new app going to get noticed?” asks Decrem.
• A short development schedule. iPhone developers had a year to play with the device before the App Store opened. They didn’t even see the iPad until Jan. 27, and except for a handful of premier developers, none have had one in hand for software test.
• A growing number of distractions. Spurred by Apple’s success, competitors from Microsoft (MSFT) and Google (GOOG) to Palm (PALM), Nokia (NOK) and Research in Motion (RIMM) have opened their own app stores. Surveying developers, Appcelerator has identified three tiers of mobile platforms: the leaders, the up-and-comers and the laggards, as shown in the graphic below. The iPad may still be a leader, but it’s got stiff competition.

Despite all this, Decrem and Lacy say they couldn’t be more excited about the iPad as a platform. They’ve submitted a new iPad music game that they hope will win Apple OK on or near April 3.

“It’s a whole new world,” says Decrem. “I think Apple has really nailed consumer behavior,” which he describes as creating content on work computers and consuming content on home computers.

“The iPad is for watching YouTube videos, updating your Facebook status, looking up something in Wikipedia, playing a quick game,” he says.

Adds Lacy: “It fits nicely with an ADD lifestyle, where you publish 140 characters at a time.”

[Follow Philip Elmer-DeWitt on Twitter @philiped]