Nope...you're right. Pretty much any of the 5 major brands that work in larger sensor cameras make a great product - Canon, Nikon, Sony, Pentax, and Olympus. And of course so do many other companies that make compact cameras...but these are 5 of the larger players in the DSLR/mirrorless/hybrid arena, and will all provide a solid, reliable product with good image quality. It mostly comes down to handling the cameras to see which are comfortable, weighing the features you need, the designs you like, the pricing being good, and any variables that might help your decision (past experience with a company, lens legacy, whatever!).
The biggest difference between the NEX5 and NEX3 is the size and build - there's very little in it, but the NEX5 is a slightly more upscale all-metal body, thinner camera and a little smaller overall, but with a more pronounced grip. Feature-wise, they're not all that different from eachother, so really the main reason to go with the 5 over the 3 is just because you favor the design or the build...and have the extra change lying around to spend!
As for the NEX vs the HX5...obviously two thoroughly different types of camera, with very different IQ. The HX5 is a solid travel camera - basically pocketable, feature-packed, small-sensored so it can provide a good lens zoom range, and basically compatible for folks looking for a second camera to supplement a DSLR, or folks looking for a compact camera to document their trips, family events, and such...but not necessarily looking to really get deeply involved in photography or expanding their skills. Not that you can't learn a lot with a compact camera, as you can...just that most people who get one aren't looking to go down that path. The NEX on the other hand is a compact and stylish all-purpose cam that can do much of what the HX5 can, but in a bulkier package - it is meant to add the sensor size and capabilities of a DSLR, but in a compact and user friendly package that is approachable for photographers and non-photographers alike. In normal daylight snaps, both could make fine prints and slideshows...start zooming in to pixel-level detail, or start moving into low light or challenging situations and the image quality will be many times greater overall with the NEX cams. The NEX cams are equal to the best APS-C sensor DSLR cameras in low light ability, so where the HX5 can nudge up to ISO400, or use special image-stacking tricks to turn out decent ISO1600 results, the NEX can be easily and casually used at ISO6400. And of course, you do have the interchangeable lenses with the NEX.
The NEX would be the better choice if you think the photography bug might hit...because it's expandable. You can add more and different lenses. You can start to use manual controls more. You can start buying various old manual lenses with adapters from almost any manufacturer. You can even buy Alpha lenses that would also work on a DSLR body, if you ever decided to go that route. You could explore low light photography. You'll have an easier go of it shooting people indoors and action or movement with the large sensor camera. But you have to accept the compromises - it isn't as compact, extra accessories must be bought to explore all the abilities, and in some cases, you might want to learn a little more of the basic tenets of photography to understand things like the much shallower depth of field the larger sensor will have. And you lose some toys - in-body stabilization, GPS, multi-image noise reduction stacking. But you gain RAW shooting ability, high ISO performance second-to-none, and interchangeable lenses.
Lots to consider!
Sony DSLR-A580 / Sony 18-250mm / Minolta 50mm F1.7 / Sigma 30mm F1.4 / Tamron 10-24mm / Tamron 150-600mm / Tamron 90mm F2.8 macro / Minolta 300mm F4 APO
Sony A6000 / 18-55mm F3.5-5.6 / 55-210mm F4-6.3 / 10-18mm F4 / 35mm F1.8 / 16mm F2.8 / via manual adapter, lots of Pentax K mount, Konica K/AR mount, and Leica M mount manual lenses