respecting river raises

[redbeard]

i believe that some very respected posters have stated that a river check raise is even stronger than a river raise. (i don't think i understand why that is) let's say for arguments sake that our opponent is unknown and the hand is heads up on the river. if we have had the initative the entire hand and he raises us on the river why is a check raise a greater indication of strength than a raise from in position? it seems to me that both raises would be an equal indication of strength one just means we are out of position (our opponent raises) and one means we are in postion (our opponent check raises). any thoughts are appreciated.