Because the remnants of Ivan are too far to the north and the trough not expected to dive far enough south to have a significant (note how I didn't say no) impact on the future track of the storm.

The system to pick up Karl is already in place there -- an upper-low to its west -- though it may become enhanced just slightly by the remnant trough from Ivan departing the eastern seaboard. Or, the trough from Ivan may ride up and over the ridge (almost a Rex block-type of pattern)...it remains to be seen. Bottom line though, Karl is one for the fishes.