lspci is wrong about Intel i5 processor on 14.04

I suggest you report a bug. Trusty is not ready and not stable.

Some addition:
Ubuntu 12.04 and older do not know name of my processor at all (It is ok, my processor is not so old)
Kubuntu 13.04, Ubuntu 13.10 and, also 14.04 name my processor as Xeon. But is it correct way to determine processor name by calling lspci?

Here some outputs for mentioned OS'es
13:10
ubuntu-studio@ubuntu-studio:~$ lspci | grep processor
00:00.0 Host bridge: Intel Corporation 3rd Gen Core processor DRAM Controller (rev 09)
00:01.0 PCI bridge: Intel Corporation Xeon E3-1200 v2/3rd Gen Core processor PCI Express Root Port (rev 09)
00:02.0 VGA compatible controller: Intel Corporation 3rd Gen Core processor Graphics Controller (rev 09)

13:04
kubuntu@kubuntu:~$ lspci | grep processor
00:00.0 Host bridge: Intel Corporation 3rd Gen Core processor DRAM Controller (rev 09)
00:01.0 PCI bridge: Intel Corporation Xeon E3-1200 v2/3rd Gen Core processor PCI Express Root Port (rev 09)
00:02.0 VGA compatible controller: Intel Corporation 3rd Gen Core processor Graphics Controller (rev 09)

12.04 and 10.04
ubuntu@ubuntu:~$ lspci
00:00.0 Host bridge: Intel Corporation Ivy Bridge DRAM Controller (rev 09)
00:01.0 PCI bridge: Intel Corporation Ivy Bridge PCI Express Root Port (rev 09)
00:02.0 VGA compatible controller: Intel Corporation Ivy Bridge Graphics Controller (rev 09)
00:14.0 USB controller: Intel Corporation Panther Point USB xHCI Host Controller (rev 04)
00:1a.0 USB controller: Intel Corporation Panther Point USB Enhanced Host Controller #2 (rev 04)
00:1b.0 Audio device: Intel Corporation Panther Point High Definition Audio Controller (rev 04)
00:1c.0 PCI bridge: Intel Corporation Panther Point PCI Express Root Port 1 (rev c4)
00:1c.2 PCI bridge: Intel Corporation Panther Point PCI Express Root Port 3 (rev c4)
00:1c.3 PCI bridge: Intel Corporation Panther Point PCI Express Root Port 4 (rev c4)
00:1c.5 PCI bridge: Intel Corporation Panther Point PCI Express Root Port 6 (rev c4)
00:1d.0 USB controller: Intel Corporation Panther Point USB Enhanced Host Controller #1 (rev 04)
00:1f.0 ISA bridge: Intel Corporation Panther Point LPC Controller (rev 04)
00:1f.2 SATA controller: Intel Corporation Panther Point 6 port SATA Controller [AHCI mode] (rev 04)
01:00.0 VGA compatible controller: Advanced Micro Devices [AMD] nee ATI Thames [Radeon 7500M/7600M Series]
03:00.0 System peripheral: JMicron Technology Corp. SD/MMC Host Controller (rev 30)
03:00.2 SD Host controller: JMicron Technology Corp. Standard SD Host Controller (rev 30)
03:00.3 System peripheral: JMicron Technology Corp. MS Host Controller (rev 30)
04:00.0 Network controller: Atheros Communications Inc. AR9485 Wireless Network Adapter (rev 01)
05:00.0 Ethernet controller: Realtek Semiconductor Co., Ltd. RTL8111/8168B PCI Express Gigabit Ethernet controller (rev 07)

lspci does not show your processor model. In this case, it is showing the name of your PCI Bridge, which is common to Xeon E3v2 and **3rd Gen Core** processor. You have a 3rd Generation Core processor, so it is correct.

Why did this change from earlier Ubuntu releases? Well, whoever's in charge of the PCI ID database thought "Intel Corporation Xeon E3-1200 v2/3rd Gen Core processor PCI Express Root Port" was more informative than "Intel Corporation Ivy Bridge PCI Express Root Port."
If you run 'sudo update-pciids' on 12.04, for example, lspci would show the updated name ("Intel Corporation Xeon E3-1200 v2/3rd Gen Core processor PCI Express Root Port").

If you really want to know what the Linux kernel reads your CPU model as, look at output of:
cat /proc/cpuinfo