Thinking back, when they bought Shake et al., they killed the Windows version and dropped the Mac OS X price tremendously to promote sales, so those might indeed be the correct pricing.
It is the correct price...they never dropped the Linux price. Before Apple owned it, licenses were $10,000. When they bought it, they dropped it to $5000. With Shake 3.5 they dropped the Mac version to $3000 and Linux/Irix to $5000. Shake 4.1 saw the Mac version drop to its present price, but there was no corresponding drop for Linux.
Some might say the current price for Shake for OSX @$499 is a super deal and the Linux price ain't half-bad considering the fact that Shake was selling for $9900 per license in '99.