The former has familiarity, business relations, and journalists are expecting to hear from them. The latter just means you're forced to end up sending unsolicited emails or contacts. You've to sell the introductions as well (then your rolodex is actually worth something).
Absolutely not true.
Journalists know they're just getting e-mails regarding any company that paid to have their message sent out, that holds no special meaning to them.
Some actually strongly prefer a letter coming from someone at the company, personalized with a 'if you have any questions please don't hesitate to ask' and a 'thank you'.
As opposed to basically 'HERE'S THE 3RD ONE WE GOT PAID TO SEND U TODAY!'.