I thought the same thing ~1 week ago when I tried just what you said but it doesn't work... gives a nasty warning message:
```
Warning: Cannot use 'in' operator to search for 'src' in addons/**/*.js Use --force to continue.
```

What you are thinking of can currently only be done as the value of a target without any `options`, etc. e.g.
```json
tests: ['test/**/*.js']
```

Talked to @cowboy about it on IRC last week to confirm.  At least 1 other Grunt collaborator thought that would be a great enhancement, though I forgot who... maybe @tkellen?