Plus further processing after the retouching has taken place, especially for web images (i.e. downsampling, compression), makes it harder to spot again.
Actually that generally does the opposite, with poor clone brushing, chop jobs, composites and high compression it will make the surrounding area "bubble" thus making the area more evident to Photoshopping.
The best ones I've seen start with a very high quality image, they save it off lower quality, up-sample then re-save in a lower quality this "normalises" the image quality therefore making it harder to pick.
The ones that get caught I can guarantee are the one that start with a standard image, splice stuff into it then save it out. The mixed quality of imagery, depth of field, proportionality and logic are generally the basic principals that determines if it looks real or fake.
For instance with Bluetooth's image the give away is the circle in the top left (logic, pattern is inconsistent), "feathering around the person" (depth of field) and no shadow (logic).