It varies with the model and in fact the COUNTRY. In the EU many camcorders stop at 30 minutes to avoid a TAX. This has nothing to do with HDD or the technology!
Didn't know about that? Read http://www.dpreview.com/news/2012/05/18/WTO-looking-at-moves-to-remove-30-minute-limit-from-digital-cameras
Is HDD a good recording format for camcorders - what video length can I get in those and does samsung make any good ones with HDD