Not true...many hosting companies have second and minute restrictions (like within one minute). But many hosting companies do allow you to execute crontab every ten minutes...at least the more reputable companies.
Thanks for enlightening me. I believe it also depends on which kind of cron event you are running. My provider permits me to build my Links database with about 3000 links once per day (takes about 8 mins). Other cron events such as sending out newsletters etc. are not restricted.