Yes you are correct. I should have said "If you have a Canon body you have to buy Canon mount lenses"
These can be made by Sigma or who ever but still you will end out with a collection of Canon mount glass and the next body you buy will be Canon. Basically you are "married" to the brand and changing is expensive.
In some cases the third party leenses are as good and cheaper. That might be the case more with Nikon
Yeah, I sort of understood you Chris, I wasn't picking a fight with my comment. I agree it will be expensive when I go up to full-frame as I switch brands, but that's okay, the APS-C lenses I'm buying now hold good value for resale. I'm definitely switching brands over to Nikon for full-frame, unless Canon really pull a rabbit from the bag in the next couple of years.