It's not just Apple vs startups. Large customers like Apple or Samsung have big advantages over smaller phone manufacturers.
Apple can always call Foxconn and tell them that they want even this barely visible detail fixed. Foxconn comes up with number for changes in the manufacturing processes ($10 million for better tooling for example) and it's done. Small manufacturers who have low margins can't justify similar attention to detail.
Or look at phones vs. other appliances that are made for smaller markets. Garmin is the dominant incumbent in portable GPS devices and even their handsets feel like garage-made prototypes compared to even the worst phone, despite being exactly the same technology except for the backlight diffuser film.
Apple can always call Foxconn and tell them that they want even this barely visible detail fixed. Foxconn comes up with number for changes in the manufacturing processes ($10 million for better tooling for example) and it's done. Small manufacturers who have low margins can't justify similar attention to detail.