The majority of the speaker building discussions on this forum relate to subwoofers. If you want to get more answers, I would suggest one of the more active speaker (not subwoofer) building forums such as over at Parts Express, DIY Audio HTGuide etc.
At a high level, one main goal of a line array (for home use) is to allow the user to essentially be in the near field of the speaker, even at normal listening distances. Also by leveraging the ceiling and floor boundaries by having a line which goes almost from floor to ceiling, you get the perceived image of a much taller line. Another benefits of is greater output and lower distortion since multiple drivers are generating the output, not just one or two.
In your pictures the one picture is just two speakers stacked on top of each other. This will certainly give you higher output but with multiple woofers and tweeters spaced far apart, lobing and comb filtering will be prevalent. If you are sitting far enough away, for example at a concert this would be OK. For the home environment this wouldn't work as well as a properly executed line array with power tapering etc or a traditional speaker.