Miranda Rights

What are Miranda Rights and why were they not read to Dzhokhar Tsarnaev, a suspect in the Boston Bombings who was recently apprehended?

Miranda Rights have to be read to every person being arrested. These rights are the whole “You have the right to remain silent” thing that we always see on the movies or TV. According to Wikipedia: “Every U.S. jurisdiction has its own regulations regarding what, precisely, must be said to a person arrested or placed in a custodial situation.
The typical warning states:
You have the right to remain silent.Anything you say or do may be used against you in a court of law.
You have the right to consult an attorney before speaking to the police and to have an attorney present during questioning now or in the future.
If you cannot afford an attorney, one will be appointed for you before any questioning, if you wish.
If you decide to answer any questions now, without an attorney present, you will still have the right to stop answering at any time until you talk to an attorney.
Knowing and understanding your rights as I have explained them to you, are you willing to answer my questions without an attorney present?
The courts have since ruled that the warning must be “meaningful”, so it is usually required that the suspect be asked if he understands his rights. Sometimes, firm answers of “yes” are required. Some departments and jurisdictions require that an officer ask “do you understand?” after every sentence in the warning.
An arrestee’s silence is not a waiver, but on June 1, 2010, the Supreme Court ruled 5-4 that police are allowed to interrogate suspects who have invoked or waived their rights ambiguously, and any statement given during questioning prior to invocation or waiving is admissible as evidence. Evidence has in some cases been ruled inadmissible because of an arrestee’s poor knowledge of English and the failure of arresting officers to provide the warning in the arrestee’s language.
There is a “public safety exception” for reading the Miranda rights. According to the Huffington Post:”The public safety exception permits law enforcement officials to engage in a limited and focused unwarned interrogation of a suspect and allows the government to introduce the statement as evidence in court. The public safety exception is triggered when police officers have an objectively reasonable need to protect the police or the public from immediate danger.”So, if the police feel they have a need to protect themselves or the public from immediate danger, they apparently don’t have to read the rights.
The question becomes: after he has been arrested, strip-searched and brought to the hospital in police custody, is there still an immediate danger to police or to the public?  Why did it take days for them to read Dzhokhar his rights?  And what kind of “answers” did they get from him prior to reading his rights?  Were his “answers” coerced?  Was he coherent?
These things are not in the mainstream news.  The best I can find is “The 19-year-old is responding sporadically in writing to questions from investigators regarding other cell members and other unexploded bombs, law enforcement officials said.”
And here’s a bizarre factoid:  How did the “public safety exception” even get enacted?  According to Techdirt, it was enacted by Obama administration, which officially created an exception to the Miranda rules (unilaterally, without court approval) a few years back – apparently in October of 2010, though news about it only came out in March 2011.  The “public safety exception” itself is suspect and was enacted in dubious ways.