Conventional wisdom might suggest that the best way to organize any web service or personal product is by allowing the user the greatest power in choosing how it is organized. Nearly any kind of consumer product nearly necessarily comes in different sizes and colors depending on the preference of the buyer, some allowing their users a free range of customizability. Online products as social media sites, blogs and other personalizable webpages can bear a theoretically infinite ability for the user to manage the appearance and nature of the site, so services that provide these have the choice of relegating a certain amount of controlability to the users. But as it happens, more user friendliness and power are not necessarily advantages beyond a superficial level.
The classic example of why this is generally true is the Great Facebook shift. When more and more social network users began to abandon their MySpace accounts for Facebook, they measurably lost customizability. MySpace allowed users to change the HTML framework of their page, allowing for plug-ins and external code. They could decorate their pages with images, even .gifs, and have their favorite songs play upon access. Yet for whatever reason, these wide liberties could not manage to spoil the appeal of the Model-T variety Facebook page.
There simply came a point where the customizability took over. Users had freedom, but freedom that became an annoyance to their friends. The enterprise of automatic music playing is not so grand when other users are listening to their own or wanting to be kept in silence. The abrasive and sassy images that decorated pages became too much, and each page gave the appearance of being an entirely different website. On MySpace, users had the ability to see how trashy their friends actually were; Facebook eliminated this problem by making all pages into a more or less cookie-cutter design. Thus it's because of this customizability that children now refer to MySpace as "ghetto."
Quite simply, when people want a mass-produced service or product, some customizability is nice for self expression and such, but opening the flood-gates to as much as possible is untenable. Take Apple/Macintosh hardware and programming, Macs are cultically beloved by their users and it's becoming more common for young people to universally favor them over IBM/Windows computers; it's not too uncommon for universities to form their public computer fleet nearly entirely out of Macs.
No doubt one of the reasons that Macs have become such an important social symbol is that they lack the customizability and individuality of other OSes and of other hardware. They all come in the same color (iPods are distinct for having two) and the ability of the user to modify user interface is intentionally stunted; instead of relying heavily on custom applications, Mac-users typically use the same factory programs.
Now of course this may not appeal to everyone, certainly not myself, but apparently for many consumers an obviously mass-produced identical product can reasonably be marketed for twice its value and still clear on the market. It should be no wonder why Apple has been so successful; it realized that sometimes what customers want is less in terms of malleability and individuality. For people who don't care to much about computing and simply want to have a device to edit (or more commonly just look at) pictures and go onto the internet, the enterprise of editing UI or the physical appearance of the computer is unnecessary and confusing.
There are many people who strongly favor customizable webpages and software, but in general, unrestrained customizability forms a sub-optimal equilibrium where everyone is mindlessly changing interface and appearance to stick out and find the "perfect" layout. When people buy or sign up for a similar product, they want a level of conformity and simplicity that could otherwise easily be perturbed by endless interface choices. These choices would only serve to distract users from the content of the service and make them feel constantly uncomfortable with their own choices.