Henderson has been denied clearance by the International Cycling Union (UCI) because, essentially, he is considered too good.
The former world scratch champion and Tour of Spain stage winner cannot ride in New Zealand's premier road race because of rules which prevent a professional cyclist of Henderson's standing riding in an event below a certain UCI rating.
The UCI ratings for multi-day events are 2. HC, 2.1 and 2.2.
The Tour of Southland is rated 2.2 and a rider like Henderson is not allowed to compete in an event at that level.
But when it comes to disgraced American Landis, there is no problem.
Landis, who has always maintained his innocence, was stripped of the 2006 Tour de France title and banned for two years after testing positive for synthetic testosterone.
The 33-year-old confirmed earlier in the month he will ride in the event which begins on November 2.
It might seem unfair to some that Henderson, who has never tested positive for performance-enhancing substances, cannot compete while Landis has been welcomed.
But the man in the middle of the debate was taking it in his stride when approached for comment yesterday.
"It is a bit of a shame," Henderson told the Otago Daily Times from Melbourne.
"Being a Dunedin boy, I would love to support a race in the area. Unfortunately, because of the status of my team, they won't let me ride in a race of that calibre."
Henderson's team manager wrote a letter to the UCI requesting dispensation, and Tour of Southland director Bruce Ross and BikeNZ did everything in their power to aid Henderson's desire to ride in the race.
"Rules are rules, I guess," Henderson said.
"But it does seem a bit silly. I'm having my off-season now, I'm not racing, I'm not training and would be turning up quite unfit. So it's not like I would have come down to win everything on my own.
"I'd just be there to support riders and help the race, but I don't think the UCI see it like that. They've just made a decision based on the rules."
While Ross was disappointed Henderson would not be competing, he remained hopeful Henderson would ride in the tour next year.
If Henderson is selected for a New Zealand team and rode in the national strip, he could ride in the tour.
Ross said there was no chance of that happening "at this late stage but, obviously, next year it is something we can work on.
"We recognise Greg as being a top New Zealand bike rider and it would have been great to have him in the field."
Henderson plans to relax and enjoy his break, with the next big event likely to be the Tour Down Under in Adelaide in January.
Fellow New Zealander Hayden Roulston is able to race in the tour because his 2009 team was a UCI pro-continental team rather than a UCI pro-tour team.
His move to Columbia will rule him out of the 2010 tour.
