You can record either HDV or standard-definition DV on a MiniDV tape - they use the same bitrate, so as far as the digital information is concerned, the HDV format is not more demanding than DV.
Having said that, when things go wrong (read: worn out or damaged tape), a bit error (dropout) in HDV material can have a much bigger impact than with DV. Look up "HDV" on Wikipedia for a more detailed explanation. Bottom line is that many people invest in higher-grade tape for HDV to reduce the probability of dropouts, and those higher-grade tapes are often sold as "HDV" tapes.
- Martin