Although you can't work with macros in excel online, you can open a workbook that contains macros—though you won't be able to see the macros. you can edit the worksheets and save a workbook containing macros in excel online.. In office sharepoint server 2007, excel workbooks that contain unsupported features like vba macros, form controls, and so on are not loaded in excel services. in sharepoint server 2010, to help users work with this limitation, excel services ignores certain unsupported features.. It will need to be done in the desktop version of excel. snippet from below link: "if a workbook contains visual basic for applications (vba) code, you can open it for viewing in the browser..
Those applications continue to use vba. office 365 2013 also has a new feature call "apps for office" and "apps for sharepoint". basically these are web based extentions using standard web technologies like html5, xml, css3, javascript, and rest apis.. This shifts the development focus from a proprietary language (microsoft visual basic for applications) to web-based languages (html, css, javascript, etc.) that enable you to use your web development skills for office development.. Yes, the excel web app cant do a lot of things the premise based excel can do, anything really with advanced charts and graphs cant be decodedwith all the office web apps, but they are a useful tool if you need to read or do basic editing..