Yes, although any difference is really hard to determine (at least to my ears). In order to double the recording time the sample rate is halved, meaning the amount of storage/memory for the recording is the same - and it's the storage that is the constraint. But halving a really fast rate is often unnoticed, especially when the looper is usually just providing background for the main event anyway (e.g. soloing over the chord pattern).

Imagine light travelled at half its speed. Would you really notice when you turned on the light switch? Now I realize that the comparison is at the end of the spectrum, but you get the point.

Or perhaps a more realistic example: mp3 is a very compressed audio format, resulting in files that are much smaller than WAV or CD-quality files of the same audio track. Yet mp3 is an extremely popular format, and you don't hear many people complaining about loss of quality - although there is some. Or how about JPEG vs. TIFF files for digital imaging? Same sort of deal.

EDIT: After posting this intially, I italicized a sentence  above. This sentence represents my understanding, and nothing more, of how the Looper feature is implemented in the Pod HD series. I have no insight into the technical details of the actual Line 6 implementation, which may be different. The rest of my statements, including the anlaogies, reflect my observations of the effect of the normal/half speed implementation.