Yes....there is a downside compared to LED. Mainly time.....huge disparity in running time vs. power source and also longevity of bulb(s). Also, some people prefer the bluish white tint of the LED to the more yellowish hue of the halogen (though the xenon halogens less so).

The technology is also newer with the LED's.....they are coming down in price as they age. There are also some newer versions of higher intensity LED's that are arguably better/brighter (and more like HID) than the halogens dollar for dollar (like the newer Cygolite Dual Cross or TridenX).

Finally, I can buy (and did) a 80 lumen luxeon K2 headlamp for around $20. For the same price you couldn't even touch the brightness with a halogen. I have a xenon halogen Princeton tec that costs three times that much a couple of years ago.....and the K2 is close to twice as bright and casts much further down the road.