The statement in question was in response to a suggestion submitted for Nokia Drive, which read:
Thank you for your improvement ideas, thus Symbian is in maintenance mode and no new features will be implement without extremely good reason ( business case). We have written down your ideas for future development if there is a chance that new features will be released.
Nokia Developer support
While Belle FP2 was rolling out to the last few Symbian devices (e.g. 701 and 808 Pureview), the Belle Refresh update was designed for older Symbian^3 devices (e.g. N8-00, E7-00, etc) which did not fulfil the system requirements for Belle Feature Pack 1. However, we have seen that many (seemingly) eligible devices have not received the firmware update.
Rather than issuing the Belle Refresh firmware update, it seems that Nokia (via Accenture) opted to circumvent the lengthy network operator approval processes by issuing the homescreen widgets, Music Player, Calendar and Social updates as application updates via the Software Update and Nokia Suite applications.
All of which points to update and development operations on Symbian being wound down as quickly as possible. In which case, quite what 'maintenance mode' will mean in practice remains to be seen.