it's a personal preference, that is actually shared by millions of users coming from Nokia phones and earlier Nokia Lumia phones. I'm thinking now you didn't come from N8 or even the 808, this last one has a camera button that launches the camera when phone is off just making a long press and that is an absolute convenience. and it was carried on to the first windows 8 phones, too(the 920 and the 820), not really sure about win 7 phones.
But just as you can see from the photo above, that is surely a high end Lumia and apparently doesn't have a camera button anymore. Maybe you're not as camera-centric as almost everyone else that owns a Nokia or a Lumia where camera is top notch that means a camera button is just way too important. imagine a compact camera with no shutter and u can tap on the screen yeah, but that's just odd. Nokia has been well known as the imaging powerhouse of the smartphones, you must know that. and a software or hardware disregard for something that important is a major blunder