Although this may end up being true (after all, a broken watch is correct twice a day) they really do not support this rumor well. Based on the standard 5 year cycle, Nintendo should be replacing the Nintendo DS in 2009 and the Wii in 2011 and, regardless of whether these systems are going to be released on the standard schedule or a year (or two) after, they are currently in a position where they have to increase their R&D budget today to release on schedule.
My personal expectation is that for TGS 2009, at (basically) the five year aniversary of the Nintendo DS, Nintendo will announce the successor to the Nintendo DS with very limited details; those details will later be fleshed out at E3 2010 and TGS 2010 and the system will be released in October 2010; quite possibly October 10th 2010 since it falls on a Sunday.
I'm a little less sure about the timing of the Wii, in part because the release of its successor is obviously further in the future. I do believe that there really isn't that big of a push to replace the Wii because of graphics improvements because the people who (probably) care the most about those improvements, and are willing to pay more than $200 to receive that benefit, have probably already bought a system this generation; on top of that, for the most part the improved performance of the HD systems has not really materialized into a major change in how games are played.
With that said, I think the main thing Nintendo is waiting for (at the moment) is for technology to improve enough that they can inexpensively produce a system that contains a desireable improvement in gameplay. The area for them (and us) where this improvement is probably easiest to track is in processing power, but I'm not too sure that the improvment in processing power is what will determine when their next system is released.