Some people still see Apple as the underdog, but this is a very, very flawed way of looking at the company. Apple currently resides in the top ten of the world's largest companies (by market capitalisation), so calling Apple small is about as accurate as calling unicorns stupid animals - it just makes no sense.
As such, it's only natural that regulators would keep an eye on Apple. However, you'd think that regulators would look into how Apple locks people into iTunes - iTunes and the iPod own 70-80 percent of their respective markets, and just as Microsoft was forced to open up for interoperability reasons, you'd think the same would happen to Apple (no, seriously - EU, where are you?).
According to the Post, however, the possible investigation has to do with Apple banning third-party development environments from the App Store. "According to a person familiar with the matter, the Department of Justice and Federal Trade Commission are locked in negotiations over which of the watchdogs will begin an antitrust inquiry into Apple's new policy of requiring software developers who devise applications for devices such as the iPhone and iPad to use only Apple's programming tools," the Post claims.
It is important to note that an investigation doesn't mean steps will be undertaken against Apple - it just means they're going to look into it. "Regulators are days away from making a decision about which agency will launch the inquiry," the further claim, "It will focus on whether the policy, which took effect last month, kills competition by forcing programmers to choose between developing apps that can run only on Apple gizmos or come up with apps that are platform neutral, and can be used on a variety of operating systems, such as those from rivals Google, Microsoft, and RIM."
As much as I disagree with Apple's restrictive App Store policies, I don't think they warrant an antitrust investigation. Apple is anything but a monopoly in the smartphone market (RIM is bigger, and Android is rising in popularity and sales like crazy), so that's not an angle. You really have to try very hard to come up with a market where Apple could be considered a monopoly, but it's possible (far-fetched-alert!): Apple owns the mobile app sales market (I warned you). Far-fetched indeed, since Android's application portfolio is growing very rapidly - App Store or no.
Taking that into account, it could very well be that the Post is trying to score a little on the wave of Adobe-Apple news. We'll know soon enough.