如果说，英文命名没有什么特定的非遵守不可的规则，英文命名其实充满了个性和随机性，提问者不会失望吧？
首先，说说提问者在问题说明中提到的几个英文名称的来历：
Quora：是从Question or Answer中抽出几个字母组成了一个新的名词来命名的；
Tumblr： 来源于tumblelogs，关于tumblelogs的来源：The first microblogs were known as tumblelogs. The term was coined by why the lucky stiff in a blog post on April 12, 2005, while describing Christian Neukirchen's Anarchaia:"Blogging has mutated into simpler forms (specifically, link- and mob- and aud- and vid- variant), but I don’t think I’ve seen a blog like Chris Neukirchen’s Anarchaia, which fudges together a bunch of disparate forms of citation (links, quotes, flickrings) into a very long and narrow and distracted tumblelog."
Jason Kottke described tumblelogs on October 19, 2005:
"A tumblelog is a quick and dirty stream of consciousness, a bit like a remaindered links stylelinklog but with more than just links. They remind me of an older style of blogging, back when people did sites by hand, before Movable Type made post titles all but mandatory, blog entries turned into short magazine articles, and posts belonged to a conversation distributed throughout the entire blogosphere. Robot Wisdom and Bifurcated Rivets are two older style weblogs that feel very much like these tumblelogs with minimal commentary, little cross-blog chatter, the barest whiff of a finished published work, almost pure editing...really just a way to quickly publish the "stuff" that you run across every day on the web."Twitter：拟声词，模拟鸟的叫声，象征清脆，简短，快捷。因而twitter的标志也是一只蓝色的小鸟~
至于英文命名的规则（其实，貌似真的没什么特定的规则= =）弱弱地说一句（欢迎指正补充）：
根据其产品的定位（虚拟也好，实物也好）来命名，其名称可以自创（自创的词语不一定非得符合英语的语法，一般把几个单词合并，或者在原有单词基础上改造）也可以利用已有的词语（例如一些地名、河流名还有神话里出现的名字及古语或小语种的名词会经常被用到）
如：
Nokia英文名的规则，是来源于芬兰一条河流的名字（其背后有芬兰当地的神话作为载体）；
Nokia的Lumia系列：Lumia 在芬兰语中有特别的含义，lumi 意思是雪，lumia 是雪的复数（芬兰人对冬季天气很熟悉）；
Android：最早出现于法国作家利尔亚当（Auguste Villiers de l'Isle-Adam）在1886年发表的科幻小说《未来夏娃》（L'ève future）中。他将外表像人的机器起名为Android。
PPS：一些英语名词确实是有其来源和背后的文化，但过于追究，钻了牛角尖就不好了 = =。
