Plot hole: When Ginger and Rocky escape from being made into a pie, it cuts to them back in the chicken coop. The movie is based on being unable to escape the coop, yet they can get back in no problem.
Plot hole: Ginger can hold Mrs. Tweedy single winged. She can also tip up a feeder full of food. So now we have clarified that she is one ridiculously strong hen, how does she need help pushing up a deck chair? 3 other chickens were able to do it with ease earlier.
Plot hole: As Rocky slides down the machine, he falls into the shaft where spinning razors almost kill him. He avoids this fate only by grabbing onto a long metal bar and sliding down a great distance to the part of the machine where the dough for the pies is prepared. He immediately sees that Ginger has arrived there, however given that the long metal bar was not there before Rocky grabbed hold of it, it is inconceivable that Ginger could have made it to the dough section of the machine. It was a direct drop down the shaft towards the spinning razors and the opening leading to the dough was well out of the way.
Chosen answer: Because he wanted them all to have something to look forward to, he didn't want to let them down. Plus Rocky is very bigheaded, it would no doubt be embarrassing for him to admit that he couldn't fly.