I wouldn't blame Sony's downfall due to DRM, lock-in, or other "Apple-like" behavior. They were doing this for decades with impunity. Likewise for marking up their products due to the good brand name they established.
I think the beginning of the downfall started with the Playstation 3. They incorrectly assumed that the PS3 would do well simply because the PS2 did well. At the time, the blu-ray format was at its infancy. To get the full benefit of blu-ray's resolution, one needed not only the player, but a 1080p TV, which was not cheap. Not to mention that people were upset that they'd have to repurchase movies they already owned on DVD.
Sony chose to "future proof" the PS3 by bundling a blu-ray player into it. Because blu-ray was so new, the cost to produce them was high. PS3 was priced high, even though according to Sony, they priced them at cost. Even though XBox didn't offer out of the box HD movie playback (they had an add-on HD-DVD drive), the gaming console was priced lower than PS3, and people FLOCKED to the xbox. Clearly consumers were not as brand-loyal as Sony anticipated.
The walkman brand was a thing of the past once iPod became the new standard. Apple struck a deal with the music labels and provided the iTunes store as an easy way to fill those iPods with music. Suddenly, just having a good hardware mp3 player wasn't enough to compete.
That means Sony's final stronghold was the HDTV. But Samsung slowly but surely made a name for itself by cranking out very high quality TV screens at a fraction of Sony's prices. Eventually, Samsung TVs became the gold standard for a quality LCD HDTV. And now that Samsung has further enhanced its brand with its Galaxy-line phones, Sony has nothing that really stands out anymore.
TLDR: it's not due to DRM or lock-in. It was because the PS3 flopped, and other companies produced either superior products, or comparable products at lower price.
The good thing about science is that it's true whether or not you believe in it. -Neil deGrasse Tyson
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