It's true, Apple geeks and hardware knowledge are an oxymoron Really... a DisplayPort OUTPUT on your monitor ? You do mean input right. I've never seen a monitor with a built-in pass-through or repeater output. Then again leave it to Apple to daisy chain monitors together... Either way I'm sure you mean output...
For one it completely changes the direction of the transfer.
DVI-D->DisplayPort is like DVI-D->HDMI. Seeing as how DisplayPort and HDMI are compatible I'm sure someone will create a dongle for you.
The other way around is less likely because of the bandwidth requirements. For one unless the DVI port supports HDCP (i.e. it's a DVI-D as apposed to a DVI-A (analog)) then it can't communicate on the bus so it wouldn't know if it could handle the signal (from a bandwidth perspective).
FYI, DisplayPort has higher bandwidth than HDMI 1.3a, which has a higher bandwidth than DVI-D...
There are a lot of cheaper monitors that do the same thing as the Apple monitor. You're taking a 500% markup for a fruit.
Can't find your answer ? Ask !
I'm pretty sure that the author means that the only cable coming OUT of the monitor has a Mini DisplayPort connector. So it's basically impossible to use this monitor with anything that does not have a Mini DisplayPort connector output on it. For example all the previsouly released Apple products.
There are barely connectors to make the new Mini DisplayPort products work with monitors other than the Apple LED one, so talking about this display working with other products is probably wishful thinking.