Welllll... as is true with a lot of products, not all items of the same kind are the same quality. Component integrity aside - fancy talk for the life span of the product - it's possible to have products that seem like they should be of the same quality... not... be the same quality. Taking the HDMI cables as an example, if the wiring inside is of a different quality, it might carry the signal better or worse than an HDMI cable of a different brand. The same goes for the quality of connector - a gold-plated connector conducts electrical signals a smidgenly bit better than your standard aluminum/whatever-plated connector.
That said, just because one brand/model of a product is more expensive than another, that doesn't mean it's going to be better. In fact, it's not all that uncommon to find products that are better quality than their more expensive counterparts. For example: Monster's Beats earphones are nice, but cost an arm and a leg. However, spend enough time researching high-end earphones, and you'll find a number of brands that are less expensive, yet provide better sound quality, with better tech.
Bottom line: It's well worth doing your research, even on things that don't seem to require it. Like HDMI cables.