Even as President Obama and public health officials called on other pharmacy chains to follow CVS, analysts noted that tobacco products are a small and shrinking share of sales for the Woonsocket, R.I., company and its competitors. Tobacco sales represent less than 2 percent of CVS Caremark Corp.'s annual revenues, and are likely to decline further as more communities across the country ban tobacco sales in drug stores. Already, Boston and 79 other Massachusetts communities, accounting for about half the state's population, have passed such bans.