the number of Russian speakers is much higher due to the fact that in the soviet times there were 300M citizens and they were all educated in russian! another 100M + studied and were able to speak in this language. 
it is highly unreasonable to have just 145M first language speaker, we are talking about language and not ethnicity there are 143M russians in russia (and they all speak in russian) plus 20M russian speakers in Ukraine (all ukrainians know russian - 46M) and all the belarussians speak in russian (10M) millions of russian speakers as a first language in central Asia and so on... 
http://www2.ignatius.edu/faculty/turner/languages.htm