@odinokij - welcome to MobileRead.
At the moment this plugin only has one special case handling for PDF formats - in all other cases it will attempt to convert to epub and then estimate counts based on that. I can appreciate how for CBR or CBZ formats another special exemption could be made using a rule like you mention to just count the image files. I don't have any CBR/CBZ myself and no-one else has mentioned it which is why it hasn't happened as yet.
I guess the only other complication around that which comes to mind is what would happen if you had configured other statistics like counting words or the readability. I think in this case those statistics should be skipped completely and only counting pages should be possible on CBR/CBZ.
I will take a look as part of the next release.