It's not so much as an agency being fussy or anything, it is simply the format of captioning which is commonly used, and has been so for many years, by professional news publishers and press photographers around the world. The first few characters of the caption quickly enable a busy news editor to identify the Where and When of an image. The rest of the caption will answer the questions What, Who, Why and How. They can then decide if the image is appropriate to their needs. The agencies which demand properly structured captions are not being petty, they are being professional.