I own a Nikon D7000 with 4 GB (Lexar) memory card. My image quality settings are JPEG, Large and image quality as optimum setting. The display on the top show remaining images count in formatted card as (#274) after clicking some shots this image count is not right. Like after clicking 10 shots it should show 264 but it still shows some other number close to 274. Whats wrong here?
That is normal.
The camera doesn't know how many images there is left, as images take up different amount of space depending on how much detail they contain. So the camera displays a guesstimate based on the free space on the card and an average size for images taken with your current settings.
If you take images with large areas of sky or other smooth areas (e.g. out of focus), you will see that the count decreases less than the number of images taken. If you take images full of details where everything is in focus, you might not even have room for the number of images that the camera initially estimated.
That count is a conservative estimate of how many pictures you can fit in the remaining space on your card, based on the maximum file size you could see with a JPEG Large.
Depending on the image data, your JPEG might end up compressing better, which would mean the count would go down by less than 1 picture.